The photofission yields of 238Pu and 239Pu were measured up to 11.5 MeV with the University of Cincinnati betatron. Corona discharge spark detectors were used to detect the fission fragments from isotopically pure foils in the presence of the very high alpha-particle activity of the plutonium. The photofission cross sections were deduced from the yields by both the Penfold-Leiss procedure and Cook's least-structure analysis. They show the onset of the giant resonance. The cross section for 238Pu at 7.5 MeV is 28 ± 5 mb and 21 ± 4 mb for 239Pu. At 11.0 MeV, the corresponding values were 303 ± 94 mb and 221 ± 69 mb. Between 7.5 and 11 MeV, the 238Pu photofission cross section is ∼35% larger than that for 239Pu.