Composition spreads of La1-x
CoO3 (LSCO) were synthesized as thermo-electric transducer material by means of combinatorial material synthesis, and information on their thermal diffusivity throughout the specimens was obtained. Meanwhile, it is anticipated that the composition spreads of LSCO have a variety of characteristic properties of light absorption corresponding to their composition, namely their compositional variable, x. Hence, we used transient optical pump-and-probe techniques in a reflection geometry to measure thermal diffusion times on LSCO. The results of signal analysis indicate that LSCO is a peculiar synthesized substance whose apparent thermal diffusivity, 1/ι, changes abruptly at the critical point, where the compositional variable x is equal to 0.3.