The main purpose of this research is to evaluate the effect of maximum size of coarse aggregate (MSCA) on the development of strength (compressive and tensile) of high strength concrete (HSC) and self compacting concrete (SCC) using locally available materials. Two sets of mixes, one for HSC and the other for SCC were prepared. Each set includes three mixes with same materials; fixed mix proportion and different MSCA (20, 14 and 10) mm. Fresh concrete properties were evaluated using slump test for HSC and slump flow, V-funnel and L-box tests for SCC. 72 cubes, 48 cylinders and 48 prisms for determination of cube compressive strength (fcu); splitting tensile strength (fs) and flexural strength (fr) respectively were fabricated from 6 batches. Concrete specimens after (7, 28, 56 and 90) days were investigated. The results indicated that it is possible to produce HSC and SCC with satisfied fresh and hardened properties from locally available materials by using coarse aggregate (CA ) with (20, 14 and 10) mm as maximum size. Based on the results of this work, workability of HSC increased as MSCA increase with using a fixed water to cement ratio and a fixed rate of superplasticizer (SP) while the fresh properties of SCC increased as MSCA reduced with using an optimum SP dosage for each mix. The results showed that fcu, fs and fr for HSC and SCC increased with the decreasing MSCA and observed as maximum at 10 mm MSCA when compared to 20 mm and 14 mm size at all ages of concrete. Based on the results, decreasing MSCA from 20 mm to 10 mm increased fcu by (11-16) %, fs by ( 5-8) % and fr by (6-9) % for HSC and fcu by (8-12)%, fs by (4-7)%, and fr by (5-8) %, for SCC for ages between 7 to 90 days. The results also indicated that the ratios of 7- day to 28- day of fcu values for HSC were higher than that of SCC and there was notable gain in fcu values after 28 days age for all mixes. Hardened HSC & SCC specimens in splitting and flexure showed similar pattern of strength development to those corresponding in compressive strength with a lower rate.