The interactions between polystyrene latex particles and ethyl cellulose (EC) with different functionalization pattern have been investigated. 3-Mono-O-EC and EC with statistical functionalization pattern in the anhydroglucose units were studied in aqueous solutions and dispersions. EC belongs to a group of polymers that phase separate upon heating. The two types of EC showed large differences in phase separation temperature, which was explained as an effect of different interactions with water due to different functionalization pattern. Both types of EC did adsorb on polystyrene particles, which indicated a favorable interaction between EC and polystyrene latex particles, however, in a different manner depending on the structure of EC. The conventionally synthesized ethyl cellulose with statistical functionalization pattern formed much stronger networks with polystyrene latex particles than 3-mono-O-EC did. The lower phase separation temperature and the slightly higher molecular weight of the conventional ethyl cellulose gave it higher preference for interacting with polystyrene latex particles to form network. Throughout the study, comparison is made with other cellulose derivatives like ethyl(hydroxyethyl) cellulose (EHEC) and carboxymethyl cellulose (CMC).