A research in cement board composite made frompuruntikus(Eleocharis dulcis) has been conducted. The aims are to determine its physical properties as variations ofpuruntikusfibers mass and NaOHimmersion time. The results were yielded 5.00 -15.15%, 0.52 -0.76 g / cm3 and 0.05 -0.18%, respectively for water content, density and thickness development. For moisture content and density values, the results were not met the standard of SNI 03-2104-1991, while for thickness development of all samples met the standards. The results showed fluctuating changes in water content, density and thickness development, which were influenced by the immersion time and mass ofpuruntikusfibers. From the results, it can be concluded that shorter immersion time and lesspuruntikusfibers yielded a smaller value of water content and thickness development, while density was become higher