Abstract: Two characteristic absorption peaks for I-O group of some substituted iodosobcn-zencs were identified in the region 320-625cm^-1 by comparing the IR spectra of the substituted iodosobenzenes with corresponding substituted iodobenzen.es. These two peaks could be assigned to asymmetric vibration v_as and symmetric vibration v_s of group in the polymeric structure of these iodosocompoumds. The cor-relation of v_IO to the substituent constants σ₁,σ_R⁰ and E_s was studied by linear regression analysis. The linear regression equations of the para substituent and meta substituent were obbtained as follows:para: v_IO= ρ₁σ₁+ρ_Rσ_R⁰+C meta: v_IO= ρ₁σ₁+ρ_Rσ_R⁰+SE_s+C