Study of geological units is one of the basic studies in many different sciences such as natural resources. The use of geological maps produced by geological survey is now the basic of geological studies in detailed-operating and investigative studies of natural resources. On the other hand, during the last years, remote sensing technology has been introduced as a new and efficient tool for geological studies that in addition to proper precision, it has other benefits such as accessibility to impassable or inaccessible mountainous regions. In this study, comparing the accuracy of existing geological and remote sensing maps of Vartavan catchment of Qazvin province has been the object of the study which was evaluated with the ground realities. So first, maps of geological survey were examined. Then, various image processing techniques including False Color Composite (FCC), Principal Component Analysis (PCA), Optimum Index Factor (OIF) and Band Ratio (BR) were used to enhance different lithological units and finally, RS lithology map of the catchment was prepared. Considering the variety of rocks and formations of the study area, the FCC and OIF techniques have respectively the most capabilities for differentiation of the rocks. Kappa coefficient of 0.39 between the two maps indicates low agreement between them. Checking the accuracy of maps based on the ground realities showed that photo-lithological map is more accurate (97.1%) compared to geological map (52.5%).