Cellulose nanocrystals (CNCs) have been studied as compatibilizers for improving the interfacial miscibility of polymer binary blends. Binary blends of water‐soluble polymers–poly(vinyl alcohol), poly(ethylene oxide), and polyvinylpyrrolidone—containing different amounts of CNC (16 and 25 wt %) were prepared by a solution casting method. For the first time, a systematic side‐by‐side comparison between the morphological, thermal, and mechanical properties of the polymer blends reinforced by CNC has been conducted. It has been determined that in the presence of CNC, the degree of crystallinity of the blend components decreased and the miscibility of the blends increased. The blends possess enhanced thermal and mechanical properties as a result of improved miscibility of the blend components. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48662.