We measured the γ-ray angular distribution from C12(α,γ0) O16 to the ground state of O16 using a pulsed α beam at Eeff=1.6 and 1.4 MeV. True events of C12(α,γ0)O16 were discriminated from background events with a time-of-flight method because of neutrons from C13(α,n)O16. The obtained γ-ray spectrum with anti-Compton NaI(Tl) spectrometers showed a characteristic line shape from C12(α,γ0)O16: the Doppler broadening and energy loss of α particles in C12 targets. A Rutherford backscattering spectrum of α particles from enriched C12 targets was measured during beam irradiation to obtain the target thickness and incident α-beam intensities. The astrophysical S factors for E1 and E2,SE1(γ0:Eeff) and SE2(γ0:Eeff), derived from the present cross sections are in excellent agreement with the values derived by R-matrix calculation of the β-delayed α spectrum of N16, and by using the asymptotic normalization constant in the R-matrix fit. © 2009 The American Physical Society.