In this work, the innovative starch microcapsules enclosed with hydrophobic carnauba wax were developed, which were applied to the modification of cellulose fibers, thus increasing the water resistance of paper by reducing water vapor transmission rate (WVTR). Carnauba wax being encapsulated by crosslinking starch was confirmed by thermogravimetric analysis. The sizes of carnauba wax-starch microcapsules depended on the weight ratio (R) of starch to carnauba wax and concentration of crosslinker. The best performance on water vapor barrier of the paper was achieved by the fibers treated with the microcapsules of larger size. The lowest WVTR was given by the handsheet treated by wet-end addition with carnauba wax-starch microcapsules at Rstarch/ carnauba wax=5%, and R crosslinker/ carnauba wax=50%, and had a value of 348 g/m2day, a 70% drop from untreated original paper which has a WVTR value of 1176 g/m2day.