This study was carried out in Erdek, Bandırma and Manyas districts in Balıkesir province in order to contribute to the bryophyte flora of northwest Turkey. In this study, 134 taxa (at species and infraspecific ranks) belonging to 40 families and 77 genera were identified. Among them 25 taxa were defined as new records for the A1 grid-square, which was adopted by Henderson. In the floristic list, all taxa with their Turkish distributions are given. In addition, some aspects of their biogeography and ecology are discussed.