This paper is for study on the leakage including with surface roughness in the valve stem system of diesel engine. This paper is for study on the oil leakage including with surface roughness in the valve stem system of diesel engine. In the leakage 1, the surface roughness was very dense, but leakage quantity of oil showed growing a trend. In the leakage 1 and 2, when the surface roughness was more scabrous, the control of oil leakage verified that fact is more advantageous. In the leakage 3, the sample verified more favorable for control of oil leakage that the surface roughness of valve stem was not soft. The experimental result of leakage 4 verified that lost a pocket effect that is a role for oil storage existing in the range of surface roughness in leakage 3. As a result, the oil leakage quantity knew increasing a tendency. In the showing from this experimental results, the condition of surface roughness being the most suitable for oil leakage control can conclude with 0.26~0.48㎛.