Geophysical research by using the gravity method has been carried out on the Ranakah child mountain and surrounding areas in Manggarai Regency of East Nusa Tenggara in June until July 2016. This research aims to know the condition of the subsurface geology of the area of research using the free air anomaly data from Sandwell and Smith 2016. The data are reduced by atmospheric correction, Simple Bouguer correction, and the correction of curvature to obtain complete Bouguer anomalies. Bouguer anomaly data brought down the field topography with continuation method down as deep as 300 m using the Magpic. Then, 2 dimensional modeling is done using the Grav2DC. The results obtained show that the geological conditions under the surface of the Ranakah Child mountaoin and its surrounding area was dominated by basalt rocks (density of ), andesite (density of ), and soil rocks (density of ). Keywords: Gravity Anomaly, 2D Modelling, Ranakah child Mountain.