ABSTRACT:   This study investigates the effectiveness of a computer assisted writing course on EFL students' writing skills. Word processing was as a basis for using computer as a writing tool in the computer –assisted writing (CAW) course (prepared by the researcher). Sample of the study was 4^th level EFL Saudi female students at college of Arts enrolled in English department .They were divided into an experimental group(n=30) and a control group(n=30). Ten CAW sessions were used. Results indicated that there are statistical significant differences between the means scores of the experimental group and of control group in favor of the experimental group. Questionnaire was filled by students after the last CAW session .Analyzing the questionnaire items' rates, it was found that students' attitudes were positive toward using computer in writing classes .Also they perceived that learning and using CAW course in their writing classes is effective and helpful in improving their writing skills in English.