TiO2 particle size in mesoscopic perovskite solar cells (PSCs) has a substantial impact on the photovoltaic performance of formamidinium lead trihalide PSCs. Anatase-TiO2 nanoparticles of different particle sizes (5, 30, 60, and 90nm) exhibited a trend of changes in photocurrent density and fill factor as well as in the quality of perovskite film. Power conversion efficiency over 11% was achieved for a particle size of 60nm.