In this study, a poly(acrylonitrile-co-N-vinyl pyrrolidone)/zeolite (poly(AN-co-VP)/zeolite) composite was synthesized by in situ free radical polymerization (FRP). The structural properties of the composite were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The characterization results indicated that the composite had a homogeneous and 3-dimensional (3D) structure. The decomposition temperature and glass transition temperature (Tg) were found as 410°C and 152°C, respectively. A poly(AN-co-VP)/zeolite composite was used to investigate the adsorption of brilliant green (BG) which is a water-soluble cationic dye. The kinetics, isotherms, and thermodynamics of adsorption were examined, and results showed that equilibrium data fitted the Langmuir isotherm model, and the adsorption kinetics of BG followed pseudo-second-order model. According to the thermodynamic properties, the adsorption process was endothermic and spontaneous. Response surface methodology (RSM), which was improved by the application of the quadratic model associated with the central composite design, was employed for the optimization of the study conditions such as adsorbent mass, time, and initial dye concentration. The RSM indicated that maximum BG removal (99.91%) was achieved at the adsorbent mass of 0.20 g/50 mL, an initial BG concentration of 40.20 mg/L, and a contact time of 121.60 minutes.