Soot accumulation in diesel engine crankcase is the dominant factor which governs engine oil drain interval. So, efficient soot elimination from crankcase oil can be a practical way to achieve drain interval extension. Combination of high performance oil filter and low soot dispersancy oil results in an effective measure to trap soot efficiently. In this paper, the behavior of newly developed high performance diesel engine oil having low soot dispersancy is reported.Prior to oil development, an evaluation method of soot dispersancy in oil was elaborated. Based on relative viscosity defined as ratio of soot containing oil viscosity to soot eliminated oil viscosity, dispersancy parameter was determined. Oil dispersancy evaluated on this parameter agreed with the results obtained from particle size analyzer.Secondly, a method to obtain oil filter soot trap rate to total soot contaminated into crankcase (trap rate) was established. For this purpose, soot contamintaion rate into crankcase oil was calculated based on an equation derived from a concept of soot balance in an engine. With this method, trap rate in diesel engine bench tests were obtained. A combination of a high-performance by-pass filter and a low dispersancy oil could raise the soot trapping efficiency.Based on these findings, we developed a low soot dispersancy high-performance oil. Detergency of this oil was evaluated by JASO diesel engine oil detergency test. Finally, the field test of 60,000 km with an engine provided with a high-performance filter using a low soot dispersancy high-performance oil was conducted. Test result showed a satisfactory level which exceeded the target value of extending drain interval.