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Lok Ulo area is a main river extended from north to South of Kebumen area. This area is famous for basement of pre-tertiary rock exposed to the surface. The evidence of fault by geology directly is difficult due to in part by thick weathering surface, and second it could be hid beneath the river. The gravity instrument of micro Gal precision is running to overcome the problem across the area where anticline valley is very subtle. The geology reconstruction is doing but the geophysics evidence is giving another solution. The anomalous of 2.5 mGal is resulting from 1.5 km downthrown block. The reconciliation finally deducted hence the fault is separating two block. Afterwards, by consequence the thickness of sedimentary rock is separating into two block, the west part and east part separating each other by fault. The vertical throw of fault show significant separating the mélange complex from the others. It is estimated from gravity data that the fault take deep seated origin. The thickness tertiary sedimentary of claystone cover the mélange (the older one) and separating each other. By consequence, the east part is thicker than the west