This study reports the results of compressive strength of cement mortars incorporating microorganism. The effect of addition of microorganism, Bacillus megaterium, on the compressive strength of cement mortar cube has been studied. Ordinary Portland cement (OPC) was used to prepare mortar with different cell concentration of microorganism in the mixing water. A significant increase in the compressive strength of cement mortar cube at different ages (3,7,14 and 28 days) was achieved with the addition of A megaterium. Increases in compressive strength were observed maximum in case of 105 cells/ml of microorganism. This improvement in compressive strength is due to deposition on the microorganism cell surfaces and within the pores of cement-sand matrix.