T his study aimed at the development of cloud computing based program on grammar achievement and vocabulary retention among third year preparatory students using cloud computing based program. Thirty -five third year preparatory students at EL-Shaheed Abd Allah Mohamed Abd Allah Preparatory School, Zagazig, El Sharkia Governorate, served as a treatment group, and 35 third year preparatory students at Sharweda Preparatory School, Zagazig, El Sharkia Governorate, served as a control group. The treatment group was taught using cloud computing based program. The control group was taught using the traditional method. Grammar test and vocabulary retention were administered to the students in the two groups as pre-post tests. The proposed program was taught over a period of month (five periods per week). Delayed vocabulary retention was administered to the students in the two groups as a delayed test, two weeks after the end of the experiment. The results of the study showed that the treatment group students outperformed the non-treatment group students in grammar and vocabulary retention tests. The researcher suggested that the EFL program based on cloud computing was effective in developing the students' grammar and vocabulary retention.