The paper deals with the strength of cement concrete by using flyash with cement in concrete. Partial replacement of cement by the use of flyash is being famous and gaining importance today, mainly on account of the improvement in the long term durability of concrete and ecological benefits. Technological improvements in thermal power plant operations and flyash collection systems have resulted in improving the consistency of flyash. To study the effect of partial replacement of cement by fly-ash, studies have been conducted on concrete mixes with 10%, 20%, 30% replacement of total cement 53grade percentage. In this paper, the effect of fly-ash on compressive strength is studied.