This study introduces a simple technique that can be used to quantitatively probe interparticle polymer diffusion (IPD) between adjacent particles in a latex film using pyrene excimer fluorescence (PEF). To demonstrate the validity of the technique, four latexes were prepared: two pyrene-labeled poly(n-butyl methacrylate) (Py-PBMA) latexes and two nonfluorescent PBMA latexes. The two pairs of Py-PBMA and PBMA latexes had similar distributions of polymer molecular weight and particle diameters. Mixtures of latex dispersions having a composition of 5 wt % Py-PBMA latex and 95 wt % nonfluorescent PBMA latex were cast into films. Fluorescence spectra of the films were acquired, and the ratio of the fluorescence intensities for the pyrene monomer (IM) and excimer (IE) was calculated to determine the IE/IM ratio. The latex films were then annealed at a constant temperature set between 75 and 119 °C. The fraction of mixing (fm), representing the amount of polymer having diffused out of a particle, was determined by monitoring the change in the IE/IM ratio as a function of annealing time. The fm profiles were then analyzed to yield the polymer diffusion coefficients, and the apparent activation energy (Ea) for diffusion was found to equal 179 ± 7 and 170 ± 12 kJ mol–1 for the high and low molecular weight chains, respectively. The c1 and c2 parameters in the WLF equation were calculated to be 11 ± 2 and 170 ± 30 K, respectively. The Ea values and c1 and c2 parameters were in close agreement with values previously found for PBMA by other techniques, suggesting that the PEF experiments provide a valid experimental means to probe IPD in latex films. The superiority of PEF over earlier procedures includes the extreme simplicity of the experimental method that involves the labeling of a single latex particle and the use of ratios of fluorescence intensity. It opens new research venues in the study of IPD during latex film formation.