A novel CTS/MFA composite was prepared by a solution reaction between chitosan (CTS) and fly ash modified by acid (MFA), and used for the adsorption of direct green BE (DG BE) and direct claret BE (DC BE) dyes. Some important conditions about preparation and adsorption of the composite were discussed in detail. The adsorption property of CTS/MFA was investigated. The results show that the obtained CTS/MFA (1:20 of CTS/FA mass ratio) has excellent adsorption properties for DG BE and DC BE dyes with adsorption capacities of 886 and 688mg/g , which are nearly 8 times higher than those of FA, respectively. The adsorption of CTS/MFA is strongly pH-dependent and the adsorption equilibrium can be reached in 90 minutes at 298K. The whole adsorption processes of two dyes fully conform to the pseudo-second-order rate model at different temperatures. The adsorption behavior can be described by Langmuir model well. It was found by the characterization of SEM/EDS and XRD that CTS was successfully loaded onto the MFA. The surface morphology of CTS/MFA changed significantly compared with that of FA, and the surface became more rough and uneven. As a cheap and easy-to-obtain composite material, CTS/MFA has a giant application potential for effective treatment of direct dye wastewater.