In this article, we report the tailoring of nanostructured mixed halide perovskite MAPb(I(1-x)Brx)(3) films with tunable band gap fabricated by anion exchange reaction. In this process, we used PbBr2 and methyl ammonium iodide (MAI) in order to fabricate mixed halide perovskite films. We have observed an uncommon shape transformation from nanocube-hollow tetraoids-nanocubes/plate. The underlying mechanism of shape transformation was discussed based on experimental results. The driving force for such shape transformation is combined effect of anion exchange reaction between I- and Br- at the solid/liquid interface of PbBr2 and MAI, and mechanical driving force exerted by the spin coating process. The shape transformation is highly reproducible, verified by two step process, dipping as well as spinning process. The best performing device using the nanostructured perovskite films in a device architecture FTO/TiO2/MAPb(I1-xBrx)(3)/Spiri-OMeTAD/Au shows a current density (J(sc),) of 23.58 mA/cm(2), open circuit voltage (V-oc) of 0.891 V and fill factor (FF) of 0.608, with a power conversion efficiency (eta) of 12.79% in forward sweep. In reverse sweep, the device shows the J(sc) (mA/cm(2)), V-oc (V), FF, and eta(%) are 23.852, 0.891, 0.716 and 15.237, respectively.