The present study was conducted at laboratory of food technology department, faculty of agriculture, Kafrelsheish University. This research was carried out study the most suitable conditions for increasing precent of resistant starch for both of rice and corn starches as they considered the main sources of starch in food industry in Egypt. The following experiments and tests were done: preparing resistant starch (RS3) through overlapping among several factors that is number of cooking cycles in autoclave, cooling, cooking time and the percentage of suspended starch of rice and corn starch in water. The resistant starch was estimated and the laboratory digestion of starch, and amylose and amylopectin content were estimated, the most appropriate conditions to get the highest percent of resistant starch (RS3) from the rice and corn starch was known. The physical properties of resistant starch was studied in comparison with native starch. The data showed that the best conditions to obtained the highest yield of resistant starch (RS3) from corn starch was after16 autoclaving- cooling cycles with 60 min autoclaving time at 1:4 starch /water ratio, this yield was 28.50 % this equal to 8.14 fold of that present in native rice starch ( 3.50 %). On the other hand, the best conditions to obtained the highest yield of resistant starch (RS3) from rice starch was after 20 autoclavingcooling cycles with 30 min autoclaving time at 1:5 starch /water ratio. At these conditions, RS equal to 6.12 fold of that present in native starch (4.90 %).