The rapid development and growth of Purwokerto requires greater groundwater resources. Research on groundwater vulnerability in Purwokerto is important in order to maintain groundwater resources, sustainability and development of the city. The approach or methods used in this research were: groundwater level measurement, geoelectric survey, and infiltration rate measurement to calculate the aquifer vulnerability index or AVI. This research uses soil infiltration rate data from the surface to a certain depth and the hydraulic conductivity of the lithologies located below the soil. The application of soil infiltration rate data and lithological hydraulic conductivity located below the soil provides a more continuous AVI level without any level voids than solely using lithological hydraulic conductivity data in the previous study. The AVI level of Purwokerto area ranges from low, moderate, high to extremely high. The level of AVI vulnerability in the lithology of the Slamet Volcano Lahar Deposits and Alluvium or its weathered soil is more varied than the lithology of the Tapak Formation and its weathered soil. This is thought to be related to variations in the composition of the components that make up each lithology which causes variations in weathering and AVI levels.