We have presented closed form solution for Blackman window function in fractional Fourier transform domain (FRFT). The closed form solution may be used for performance improvement in Orthogonal Frequency Division Multiplexing based communication system. Moreover, they may be useful for real-time processing of non-stationary signals. One can see from simulation results that as the value of the tunable parameter α of the FRFT is increased from 0 to 1, reduction in side-lobe levels takes place which in turn broadens the main-lobe width, thus trade-off is evident and one can chose the best window function according to the desired application.