The purpose of this study was to investigate the effect of discourse-based grammar teaching on reducing grammatical errors in English language majors' writings. The study employed the pretest-posttest control group design. Participants were 60 second year English department general education students at Faculty of Education, Ain Shams University who were divided into an experimental group (30 students) and a control group (30 students). Instruments of the study included a list of grammatical errors that occur frequently in second year English department students' writing, and a pre-post writing test that measures the frequency of those grammatical errors. The pre/post writing test was pre administered to both the control group and the experimental group. Then, the experimental group was instructed through the discourse-based grammar teaching program to reduce their grammatical errors in writing (i.e., tense errors, agreement errors, article errors, preposition errors, and sentence mechanic errors) whereas the control group was taught conventionally. The writing test was post administered to the control and experimental groups. Findings of the study revealed that the discourse-based grammar teaching program proved to be statistically effective in reducing the grammatical errors of the experimental group students' writing.