One of the most important environmental pollutants is azo dyes in textile wastewater. In this study, the removal of azo dye Acid Red 18 (AR 18) with initial concentration of 25-100 mg L−1 in aqueous solution by the adsorption process onto activated charcoal prepared from almond shell (AC-AS) was investigated. The effects of initial pH (2-12), contact time (15-120 min), adsorbent (0.2-2 g L-1) and initial concentration of AR 18 (25-100 mg L-1) on the removal efficiency of AR 18 solution were investigated. All experiments were performed on a synthetic wastewater. The efficiency of dye removal and Freundlich and Langmuir adsorption isotherms were compared as a function of decolorization and adsorption and kinetic behavior of AR 18. The maximum removal efficiency of AR 18 (i.e., 90.83%) was occurring with pH 2, contact time of 60 min, initial dye concentration of 75 mg L-1 and the adsorbent dose of 0.8 g L-1. The removal of AR 18 followed the Frundlich isotherm model (r2>0.994). Fitting of obtaining data onto kinetic models showed the pseudo second-order reaction kinetics with respect to the dye concentration. This investigation revealed adsorption onto activated charcoal prepared from almond shell presents good efficiency for solution decolorization.