We report a comparative study of the crystal structure and magnetic properties between (001) oriented epitaxial BiFeO3films grown on NdGaO3 and SrTiO3 substrates without any magnetic parasitic phase. The 15nm BiFeO3 film deposited on a NdGaO3 substrate shows substantially high magnetization (∼250 emu/cc) as compared to an identically thick BiFeO3 film (∼100 emu/cc) deposited on a SrTiO3 substrate. Detailed structural analysis revealed that the high magnetization is associated with a monoclinic (Cm) like distortion of the BiFeO3 crystal structure. We corroborated our experimental findings with first principles density functional theory calculations which suggested a saturation magnetization (266 emu/cc) close to the experimentally obtained one and a ferromagnetic ground state with the high spin moment in the Cm phase. © 2019 Institute of Physics Publishing. All rights reserved.