This study aimed to investigate the effectiveness of using computerized educational games on developing aspects of English grammar for deaf ninth graders' in Gaza Governorates. To achieve this aim, the researcher adopted a quasi experimental approach. The sample of the study consisted of (16) deaf students;(4) males and (12) females from Atfaluna Society for Deaf Children in Gaza governorate. The computerized educational games were used in teaching aspect of English grammar for the experimental group in the first term of the school year (2011-2012). A grammar test of six questions with (30) items was designed and validated to be used as a pre and post test to measure any possible differences between the mean scores of the students in the pre and the post test. The collected data were analyzed and treated statistically using T. test and the Modified Gain Ratio equation was used to measure the effectiveness of using computerized games on developing aspects of grammar for the deaf students . The study results indicated that there were statistically significant differences at (α ≤ 0.05) between the deaf ninth graders mean scores in the per test and the post test due to the use of the computerized educational games. Also, there were no statistically significant differences at (α ≤ 0.05) between the deaf students of the experimental group in the mean scores in the pre test and post test due to the gender factor. In the light of those results, the study recommended the necessity of implementing computerized games in teaching English grammar to make better outcomes in deaf students' achievement of English language. Also, the researcher suggested that further studies should be conducted on the effectiveness of computerized games on other grammatical lessons and other school subjects as well.