Photoinduced electron transfer from anthracene (An), 3-(9-anthracene)propyltrimethylammonium bromide (APTAB), and pyrene (Py) to methyl viologen (MV2+) in polystyrene (PS) latex dispersions has been studied by steady-state fluorescence, time-resolved fluorescence, and diffuse reflectance flash photolysis spectroscopy. Steady-state fluorescence measurements showed that the photoinduced electron transfer from APTAB and Py to MV2+ is remarkably enhanced on going from the aqueous homogeneous solution to the latex dispersion, whereas no such significant latex effect is observed for the An-MV2+ pair. This seems to be because An molecules deeply penetrate into the latex particles in contrast to APTAB, Py, and MV2+. The fluorescence decay curves of APTAB in PS latex dispersions are conformed to double-exponential functions. The analysis reveals that quenching of APTAB fluorescence by MV2+ (i.e., photoinduced electron transfer from the former to the latter) on PS latex surfaces is performed by both static and dynamic mechanisms. The diffuse reflectance laser flash photolysis study revealed that back electron transfer from the MV.+ cation radical to the Py.+ cation radical is markedly suppressed in the PS latex dispersion.