Photoinduced electron transfers (PET) from pyrene (Py), 1-pyrenemethanol (PyM), and 1-pyrenebutyltrimethylammonium bromide (PBTAB) to alkyl viologens, such as methyl viologen (MV2+) and Octyl viologen (OV2+), in polystyrene latex (PSL) aqueous dispersions have been studied by steady-state fluorescence, time-resolved fluorescence, and adsorption/desorption measurements. From steady state fluorescence measurements, it is found that the PET is remarkably enhanced on going from the aqueous homogeneous solution to the latex dispersion. The PET efficiency increases with increasing polarity of the electron donors in the PSL dispersions; PBTAB shows the highest efficiency and Py shows the lowest one. The low PET efficiency of Py in the PSL dispersion is attributed to penetration of Py, as revealed by the I-1/I-3 ratio in the vibronic fine structure of Py fluorescence spectrum. The PET efficiency of PBTAB in PSL dispersion increases with the increase in the charge density of the particle, but decreases with the increase in alkyl-chain length of the quencher. The alkyl viologen with longer alkyl-chain weakens the PET efficiency by desorbing the donors from the latex surface and/or preventing the donors from effective approach with higher steric hindrance effect.