Herein, the presented approach was investigated a unique technique for manufacturing water repellent/UV-protective cotton fabrics through in-situ/thermal polymerization of benzoxazine (BZs) within cotton matrix. Two BZs abbreviated as Ph-p-BZ and Ph-o-BZ were initially synthesized, and their chemical formulas were verified with FTIR, ¹HNMR, and ¹³CNMR spectral mapping data. For Ph-p-BZ, the endothermic peak was observed at 65 ᵒC, to indicate its highly/purified crystalline structure. DSC data for poly-(Ph-p-BZ) and poly-(Ph-o-BZ) showed that, their high Tg was estimated at 210 ᵒC and 195 ᵒC, respectively, due to their highly crystalline/cross-linked network structure. In-situ/thermal polymerization of Ph-p-BZ and Ph-o-BZ as within cotton matrix was subsequently proceeded. Contact angle was observably increased to 125.0° for the fabric coated with four layers of poly-(Ph-p-BZ) (cotton modified with four …