To improve the electroluminescence efficiency of organic-inorganic hybrid perovskite (OIP) films, we need to consider several different types of post-treatments after film formation such as thermal annealing and solvent annealing. Here, we only applied thermal treatment on the film excluding all the other treatments. Then, we analyzed the effects of annealing time t(ann) on crystallinity of methylammonium lead bromide (CH3NH3PbBr3) films and on luminous efficiency of CH3NH3PbBr3-based perovskite light-emitting diodes (PrLEDs). When thermal annealing of CH3NH3PbBr3 films was conducted at 90 degrees C, t(ann) <= 10 min increased its crystallinity by eliminating residual solvent and completing the conversion of precursor to crystal, but t(ann) > 10 min reduced crystallinity and caused slight sublimation of CH3NH3Br. This was consistent with trend of the luminous efficiency of our PrLEDs that showed the optimum performance at t(ann) = 10 min. These results demonstrate that optimizing tann of CH3NH3PbBr3 films is a simple way to improve the luminous efficiency of PrLEDs by controlling their crystallinity. (C) 2016 Elsevier B.V. All rights reserved.