This paper reports selected findings of a research study investigating the effectiveness of self-acces CALL program to assist Indonesian students to improve their mastery of English grammar. The data were elicited using a time-series experimental design from Indonesian students participating in a university preparation program in Australia. The result of the analysis suggest that a self-access CALL program in benefical for enhacing the mastery of English grammar, particularry in the EFL context.This paper also documens the long-lasting duration of the effect to the self-access CALL instructions.The implications for the possibility of the developement of self-access CALL in indonesia are explained.