Eddy diffusivity D_tα and turbulent Schmidt number Sc_tα (α = A,B,R) in a planar liquid jet with a second-order chemical reaction (A+B → R) are experimentally investigated. Species A is premixed in the jet flow and species B is premixed in the main flow. The concentrations of reactive species and the streamwise velocity are simultaneously measured by combining I-type hot-film anemometry with an optical fiber probe based on the light absorption spectrometry. Eddy diffusivity and turbulent Schmidt number on the jet centerline are estimated from the results of the simultaneous measurements of concentration and velocity. The results show that the chemical reaction makes Sc_tA large, and Sc_tB has a negative value in the region where the mean concentration of species B decreases in the downstream direction whereas Sc_tB for the nonreactive case has a positive value in the whole region on the jet centerline. It is also shown that Sc_tR has a positive value in the upstream region whereas it has a negative value in the downstream region. The difference in Sc_tB between the reactive and nonreactive cases becomes small in the downstream region. These results imply that the gradient diffusion model using the global constant turbulent Schmidt number poorly predicts the turbulent mass flux for reactive flows.