The present study investigated the effect of online collaborative ProjectBased Learning (PBL) on the language performance and attitudes of intermediate level students at the College of Applied Sciences in Oman. The study is a quasiexperimental study and the population of the study consisted of 255 Intermediate level students in Nizwa College of Applied Sciences in the academic year (20122013). These participants were in their foundation year and they were taking the Academic English Course during the time of the research experiment. The sample consisted of four classes (93 students), two classes were assigned to the experimental group (46 students) and they were directed to collaborate online in doing their research projects. The other two classes were assigned to the control group (47 students) and they used the traditional method and they did their projects individually. A language test containing reading and writing questions, an attitude questionnaire, students' projects' scores and messages' transcripts of focused group discussions were used to collect the data needed to answer the research questions. The major findings of this study are as follows: 1. There were statistically significant differences between the writing post-test results of the students in the experimental group and those who were in the control group in favor of the experimental group. 2. There were no statistically significant differences between the reading post-test results of the students in the experimental group and those who were in the control group. 3. There were no statistically significant differences between the projects' mean scores results of the students in the experimental group and those who were in the control group. 4. There were no statistically significant differences between the language attitudes' mean scores results of the students in the experimental group and those who were in the control group. In the light of these findings, recommendations and suggestions for further research were provided.