In recent decades, the use of synthetic polymers due to the great variety and special properties has significantly increased. Using synthetic polymers has increased environmental pollution. In order to solve this problem many studies have been reported, including the use of biodegradable polymers or biodegradable synthetic polymers with modified chemical structures. So natural polymers, especially starch, are good candidates for replacement or modification of synthetic polymers. The problem is that the starch is very brittle and little processable. For this reason, research was done to resolve the weaknesses of the process-ability of starch. In this way, in present study, graft copolymerization of starch- poly (methyl methacrylate) (starch-g-PMMA) was carried out by slurry polymerization method and potassium persulfate was used as initiator. Response surface method (RSM) was used to optimize the process parameter conditions for high grafting percent. By this method, the effect of temperature, time, ratio of monomers to starch and ratio of initiator to monomer on the conversion percentage and percentage of grafting were investigated. Analysis of variance (ANOVA) was performed on the resulting data. Result showed that the maximum grafting (45%) obtai at reaction temperature (75?C), reaction time (3 hr), ratio of monomers to starch (70%) and ratio of the initiator to monomer (2%). To evaluate grafting percent, conversion and percentage of homopolymer, gravimetry method was used. For isolated homopolymer part, extraction method carried out in soxhlet apparatus by using acetone as a solvent. Fourier transfer nfrared spectroscopy (FTIR) was used to confirm the grafting of samples. FTIR spectra of extracted samples showed a peak at 1730 cm -1 as evidence on the grafting of PMMA on starch. Scanning Electronic Microscopy (SEM) micrographs before and after extraction of samples showed the presence of patches of PMMA on the surface of bulk starch and the granule morphology of starch had been destroyed by slurry copolymerization. Also the effect of esterification of starch by maleic anhydride for surface modification of starch on grafting of starch was investigated. Differential Scanning Calorimetric analysis (DSC) and Thermal Gravimetric Analyses (TGA) were used for investigation of thermal behavior of samples,. The results of DSC analyses suggested that the esterification modification and graft polymerization decrease the crystallinity degree of native starch and also it destroys some of crystal structures of native starch. Also the peak of amylose-complex melting of starch shifted to high temperatures by graft polymerization. TGA analysis of samples indicated that the grafted starch and grafted modified starch show a two-step thermal degradation. Thermal stability grafted starch was increased, while thermal stability of esterified starch decreased. Melt Flow Index (MFI) of samples showed that by increasing the percentage of grafting, MFI of the copolymer was increased and the processing properties of product were improved, consequently. Keyword : Starch, PMMA, Slurry polymerization, Response Surface Designs, Processability, Maleic anhydride