In this study, corn cobs and corn roots, agricultural by-products and wastes, were used as precursors for preparation of powder activated carbons (PAC-CC and PAC-CR) by chemical activation with H₃PO₄. Functional groups on the surface of both adsorbents were determined by using ATR−FTIR spectroscopy, while their specific surfaces area were calculated using methylene blue adsorption method. Removal of Crystal Violet (CV) dye from aqueous medium onto both adsorbents was carried out at optimal pH of 10. The pseudo-first order and pseudo-second-order models were used to study adsorption kinetics. The Langmuir and Freundlich, isotherm models were employed to analyze the adsorption isotherm. CV dye molecules-activated carbon surface interaction revealed CV dye’s monolayer formation over activated carbon’s surface and the involvement of chemisorption, as verified by Langmuir isotherm model and pseudo-second order model, respectively. Langmuir maximum adsorption capacity of PAC-CC and PAC-CR for CV dye were 41.80 mg/g and 35.92 mg/g, respectively. From these results, it can be concluded that the activated carbon prepared from corn cobs or roots as precursor can be used as adsorbent for successful removal of dyes in an aqueous medium.