The present study investigated the effect of implementing a Process PortfolioBased Writing Assessment (PPBWA) method on EFL 11 graders' writing performance and attitudes and was packed up with their teachers' views on the experimented method. The study adopted a quasi-experimental design with a pre-test/posttest control group to deal with the quantitative part and was supplemented with a qualitative part to deal with the students' and teachers' views on the use of PPBWA. The sample of the study consisted of 4 grade 11 A (post-basic) classes (each with an average of 22 students) from two schools in the Batinah North Governorate, drawn from the whole population of Grade 11A female students who were registered in the academic year 2012-2013 in the governorate. Two of the classes represented the experimental group with 45 students and they received the treatment (being instructed and assessed using PPBWA). The other two classes represented the control group with a similar number of students and continued to study writing in the traditional way (following the productapproach to writing). Instruments for data collection for this study, which lasted for 13 weeks, constituted a writing achievement test (pre-test/posttest), two students' attitudinal surveys and a semi-structured teachers' interview. The test was used to measure learners' level in writing before and after the experiment to determine their level of improvement at the end of the PPBWA course which lasted for thirteen weeks. To verify the test results, the experimental group's initial and final course assignments were also compared. One of the students' attitudinal surveys targeted collecting quantitative data on both groups' attitudes towards writing in English while the other targeted collecting similar data on the experimental group's attitudes towards PPBWA. Part of the second survey targeted collecting qualitative data on the experimental group's viewpoints regarding the challenges and benefits of PPBWA. Teachers' semi-structured interview aimed at gathering further information on the same issues from the point of view of the teachers to pack up the study findings. The major findings of the study are as follows: Results of the achievement test indicated better performance of the experimental group in their general writing achievement as well as their achievement in each of the sub-skills of organization, grammar, vocabulary and mechanics. This indicates that using PPBWA was helpful in improving students' writing. Comparison of the experimental group's first and final writing assignments revealed a significant improvement in their writing performance, which supports the previous result. When comparing the attitudes towards writing of the experimental and control groups, it was found that the experimental group's members have developed a more positive attitude. Their attitude has raised significantly compared to that of the control group and their own initial attitude (before receiving the treatment of PPBWA). Also, a noticeable positive attitude towards PPBWA was developed by the members of the experimental group, who liked the new method and expressed their desire to continue with it in the future. From learners' point of view, PPBWA was beneficial as it helped them discover some of their strengths and weaknesses in writing, develop better writing skills, I develop closer relationships with teachers in a more relaxing and engaging atmosphere, become more independent and responsible for their own learning and • develop new learning strategies Learners shared a number of concerns like drafting, maintaining a balance between the writing requirements and the other subjects' assignments and projects, shortage of time, doing self-assessment and organizing the portfolio contents. Teachers of the experimental group also developed a positive attitude towards PPBWA which they enjoyed. They confirmed its usefulness in developing learners' writing skills, increasing students' active participation in class, raising and developing learners' critical thinking. Teachers' concerns include difficulty in changing the attitude of weak learners to get involved and some students' dependence on others to do their work. In light of the research findings, implications and recommendations for further research were outlined.