Modification of fly ash into pellets could be conducted by compositing using crosslinked chitosan-glutaraldehyde. Fly ash composite pellets and chitosan could be used as adsorbent of Hg2+ in the liquid with variation of fly ash and chitosan mixtures crosslinked to glutaraldehyde. The mass variation of fly ash was 2 g, 3 g and 4 g in 20 mL chitosan solution. Characterization of adsorbent was conducted by FTIR and Gas Sorption Analyzer to determine the pore character of fly ash, chitosan and adsorbent composite. The results showed that adsorbent with 3 g fly ash in the 20 mL chitosan solution has the largest surface area and pore total volume for 30.97 m2/g and 4.54 cc/g, respectively. Whereas the smallest pore average radius is 29.31 Å. Identification of fly ash-chitosan composite functional groups from infrared spectra indicate the presence of functional groups to absorb Hg2+ which can be seen at wave numbers 3433 and 2932 1/cm.