Two kinds of dehydroalanine monomers, N-isobutyryl dehydroalanine (iBDHA) and its methyl ester (iBDHAM), were synthesized and their homopolymers were prepared by free radical polymerization. While poly(iBDHA) did not show any phase transition in water, poly(iBDHAM) exhibited the lower critical solution temperature (LCST) at 19 degreesC to form colloidal dispersion of nanoparticles with 60 nm diameter above the LCST. This nanoparticle formation was thermoreversible.