This study reports a new inorganic-organic composite membrane fabricated by an electrostatic self-assembling method. The low-cost and eco-friendly porous geopolymer (PG) was chosen as a support, on which chitosan (CS), a "green" biomaterial, was used to form an active layer. With optimum dosage of CS (2.0 mL of 1.0% CS solution), the obtained CS/PG membrane exhibited a high porosity of 50.97% with an average pore diameter of 13.93 nm as well as a high water flux of 1663.82 ± 22.46 L/m·h·bar. The effects of initial concentration, pH, flow rate and temperature of the feed solution on crystal violet (CV) removal by the CS/PG were evaluated in a continuous mode. The results indicated ~95% CV could be removed from water during continuous treating of 14 h. The effectiveness in CV removal by the CS/PG membrane was attributed to the synergistic effect of rejection and adsorption. Furthermore, the composite membrane could be easily regenerated for prolonged use. Overall, this work opens a new possibility of building cost-saving and eco-friendly composite membranes for practical applications in water purification.