We analyze the periodicities for 294 solar flares observed by Nobeyama Radioheliograph over 6 discrete frequencies of 1, 2, 3.75, 9.4, 17 and 35 GHz during the solar cycle 23 between 1998 and 2004. Using Fourier analysis, we pick up the shortest period ($T_{\rm{s}}$) for each event at each frequency channel. We find that $T_{\rm{s}}$ varies in the range of 0.25–0.62 s over 6 frequency channels.