Aleppo pine-tree sawdust, a forest waste abundantly available in Algeria, was used for the adsorption of CI Basic Blue 3 from an aqueous solution. The effects of adsorbent dosage, pH, adsorbate concentration and contact time were studied. The equilibrium adsorption data were analysed by Langmuir, Freundlich and Temkin isotherm models. It was found that the Langmuir isotherm fitted well to the observed data for CI Basic Blue 3 adsorption onto Aleppo pine-tree sawdust based on the correlation coefficient R2 and four different error functions for the non-linear regression. The adsorption capacity of Aleppo pine-tree sawdust for CI Basic Blue 3 was determined with the Langmuir model and was found to be 65.36 mg g−1 at 293 K. The adsorption kinetic data were modelled using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic equations. It was seen that the pseudo-second-order equation could describe the adsorption kinetics and intraparticle diffusion was not the sole rate-controlling factor. The results indicated that Aleppo pine-tree sawdust is an attractive alternative for removing cationic dyes from wastewater.