Bismuth magnesium titanate thin films were prepared on platinized silicon wafers via modified sol-gel deposition method. Highly dense samples with pseudo-cubic structure were obtained under proper thermal treatment technique. Electric breakdown strength was dependent on annealing temperature which resulted in the variation of energy storage performances. The optimal charged energy storage density W-c 47.8J/cm(3) and recoverable energy storage density W-reco 26.0J/cm(3) of the 640 degrees C annealed films at 100Hz were achieved, respectively. This dielectric film can be a promising candidate for high voltage lead-free energy storage applications due to their excellent performances.