The transport of photogenerated electrons in nanoporous TiO2 electrodes is examined in a lithium perchlorate electrolyte solution by laser-induced photocurrent transient measurements. The diffusion coefficients of the photoelectrons are found to depend not only on electron density but also on the lithium ion concentration in the solution. The behavior of diffusion coefficients depending on lithium ion concentration is interpreted with an ambipolar diffusion mechanism. Diffusion coefficients at a high photoelectron density were observed to level off at a low lithium ion concentration, which is attributed to the effect of an ambipolar diffusion mechanism.