Dispersion in optical fiber is a noteworthy issue in optical communication system. This paper is focused on reducing the effect of dispersion by utilizing a MZM with negative chirp. The modulations that are used in this paper are ODSB and OSSB modulation systems. While analyzing the results that obtained by varying chirp and extinction ratio parameters in ODSB and OSSB modulation system, the dispersion is reduced for negative chirp value. The RF frequency is chosen as 18GHz for better performance. On comparing ODSB and OSSB modulation system the power degradation is minimum in OSSB system than ODSB system.