Much research had established the use of major crops as an additive and/or replacement in the construction. This study utilized and determined the optimum amount of rice husk ash (RHA) and sugarcane bagasse ash (SCBA) as partial replacements of cement in a 1:4 ratio of cement to the sand mixture in developing concrete hollow blocks (CHB) by testing its compressive strength, water absorption, and fineness of cement mixture. Five set-ups were identified in this paper in terms of percentage replacement on the amount (0%, 2.5%, 5%, 7.5%, and 10%). The result showed an increase in fineness residue from 0%-10% cement mixture. The compressive strength test results showed an increase in compressive strength of 0-10%, with a significant drop at 7.5%. On the other hand, the water absorption test displayed an increase in moisture content from 0% to 10% replacement. 86.67% have met the DPWH and ASTM strength requirements, and all cement mixtures are below 10%, not exceeding the minimum requirement. Further analyses of the results were discussed as well. In conclusion, 5% each of RHA and SCBA was used as the optimum replacement to cement in terms of compressive strength for non-load-bearing CHBs.