One of the long-standing challenges in studying structure-property relationships in latex films is to directly characterize the size and morphology of the corresponding polymer particles, especially the particles with low film formation temperatures. Here we present an in situ transmission electron microscopy (TEM) study that allows characterization of film-forming latex particles in solution. Liquid cell TEM provides the opportunity to image latexes with a range of particle sizes and glass transition temperatures. Together with a staining technique, it can also be used as a tool to characterize the internal structure of particles in solution.