This study investigated the ideal conditions for achieving fully deacetylated chitosan from shrimp and crab shell detritus. The deacetylation method consisted mainly of two steps, heating the decolorized chitin at 100 ºC for two, four, and six hours, then cool-stirring at 200 rpm for zero, two, and four hours. The maximum degree of deacetylation (DD) resulted from 6-hours of heating and 4-hours of cool-stirring. The highest DD, determined by the potentiometric titration method, FTIR, and 1H NMR of shrimp chitosan recorded 97.2%, 98.8%, and 96.39%, against 99.8%, 100%, and 100%, for crab chitosan, respectively. The physicochemical properties of the chitosan with the highest DD have were elucidated by X-ray, FTIR, 1H NMR, and SEM. The X-ray, FTIR, and 1H NMR analysis confirmed the preservation of the identical structure of the prepared chitosan. The prepared shrimp chitosan exhibited 96.5% solubility, 548.71% WBC, and 499.60% FBC, compared to 99%, 475.88%, and 495.84% for crab chitosan, respectively.