This study investigated the morphotectonic evidence from the southern branch of the North Anatolian Fault (NAP) and the south Marmara sub-region, NW Turkey. The south Marmara sub-region has two uplifts located in the south and north, and a depression between these uplifts. The uplifts are bounded by the southern branch of the NAF. The southern branch is divided into the Yenice-Gonen (YGFZ), Manyas-Mustafakemalpasa (MMF), Uluabat (UFZ) and Bursa (BFZ) faults. The relation between the active tectonics and recent morphology were evaluated by using the geomorphic indices (GIs) (AF: asymmetry factor, T: topographic symmetry factor, SL: river length-gradient index, S-mf: mountain-front sinuosity). GIs were used to define the effects of tectonism on morphology and were used to calculate the relative tectonic activity index (Iat). The values obtained through the GIs indicate a young tectonism in the study area. The study area morphometrically presented two Iat classes; class 1 (high relative tectonic activity) and class 2 (moderate relative tectonic activity). The present GPS data and Iat classes of the southern branch faults of the NAFZ were correlated. All of the calculations and field data reveal that the southern branch of the NAF is the main tectonic element forming the geomorphology of the south Marmara sub-region. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.