Gamma ray induced decomposition of double nitrates of bismuth with transition metal ions with the composition 3M^II(NO₃)₂ • 2Bi(NO₃)₃ • 24 H₂O (M^II = Co, Ni, Cu, Zn, and Cd) has been studied over a wide absorbed dose range up to 700 kGy at room temperature. G(NO₂^-) values depend on the nature of transition metal ion and absorbed dose. G(NO₂^-) values for double nitrates of Ni-Bi are higher but Cu-Bi exhibits low G-values. Further G-values of the double nitrates are lower compared to either of the nitrate salts.