This study aimed to examine the level of teacher competencies in educational assessment in grades (7-12) as viewed by educational supervisors and teachers in Sultanate of Oman. It also examined the effects of some demographic variables, including gender, specialization Islamic Studies, Arabic language, English language, Science, Mathematics, Social Sciences ) and profession experience ( 1-5, 6-9, more than 10 years) on the level of educational assessment competencies. The sample consisted of two groups The first group consisted of (71) educational supervisors, and the second group consisted of (677) teachers. A questionnaire was used in order to investigate the level of educational assessment competencies. The questionnaire consisted of (59) competencies which were divided into seven domains; each domain represented one of the standards of educational assessment competencies developed by NCME. The domains are : 1- selecting assessment methods, 2- developing assessment methods, 3- administering ,scoring and interpreting results, 4- using assessment results in decision making, 5- grading, 6- communicating assessment results, 7- ethics in assessment. This questionnaire was reviewed and validated by a number of experts at department of psychology in Sultan Qaboos University and General Directorate of Educational Assessment in Ministry of Education. In addition, the cronbach-alpha reliability coefficient was computed and reached (0.96). The data were statistically analyzed using means, standard deviations, pearson correlation and multivariate analysis of variance. The results indicated that: 1- There is a statistically significant difference at level of (0.05) between educational supervisors and teachers on rating the level of educational assessment competencies for teachers of (7-12) grades in all domains. These differences were favoring teachers. Teachers of grades (7-12) have medium level of assessment competencies as rated by educational supervisor, while they have high level of assessment competencies as rated by teachers. 2- The highest level of educational assessment competencies that was rated by supervisors was for the domain of ethics in assessment followed by developing assessment methods, grading, using assessment results in decision making, selecting assessment methods, administering, scoring and interpreting results, and communicating assessment results. 3- The highest level of educational assessment competencies that was rated by teachers was for the domain of developing assessment methods followed by ethics in assessment, grading, selecting assessment methods, using assessment results in decision making, communicating assessment results, administering, and scoring and interpreting results. 4- The results also showed that there were statistically significant differences related to gender in favor of females on all domains, but there were no statistically significant differences on all domains related to profession experience and specialties .