Nanocrystals of octadecyl acrylate 1, octadecyl methacrylate 2 and N-octadecylacrylamide 3 were prepared by the reprecipitation method as water dispersion for the first time. Their sizes were from 120 nm to 350 nm depending on the preparation conditions. Although polymerization of 1 through 3 in nanocrystals was essentially the same as that in bulk crystals, it is interesting that 1 showed smaller average molecular weight and dispersity index in nanocrystals compared with in the bulk crystals.