Saudi students encounter many problems in writing skill as several studies revealed (e.g.Alhazmi, 2006; Alsamdani, 2010). Providing effective and useful feedback may help to overcome these challenges. Therefore, this study examines the effect of teachers' written corrective feedback on female Saudi EFL students' written essays and to what extent it affects students' written grammatical and lexical accuracy. The sample comprises 50 foundation level students, across two groups: an experimental group (n=29) and a control group (n=21). Data were gathered over a 10-week period using a pre-/post-test/delayed post-test design for comparable groups. The findings show that although many errors were made in the writing performances, the students in the experimental group had significantly better achievements than the students in the control group on the measure. The results lend support to the efficiency of teachers' written corrective feedback, showing it has a significant positive effect on the participants' grammatical and lexical accuracy.