This study presents 5-hydroxymethylfurfural removal from waste hand paper hydrolysate using activated carbon adsorption. In this context, the effects of adsorbent dosage, initial 5-hydroxymethylfurfural concentration, temperature, and agitation speed on 5-hydroxymethylfurfural adsorption were investigated. Moreover, isotherm and kinetic evaluations were performed using Langmuir, Freundlich, and Temkin models. The experimental data were correlated with zero, first, pseudo-first, and Weber–Morris intraparticle diffusion models. The toxicity of 5-hydroxymethylfurfural was determined using the resazurin reduction assay, and the EC50 of 5-hydroxymethylfurfural in the hydrolysate was found as 192 mg/L. Most convenient 5-hydroxymethylfurfural adsorption was obtained at 5 g/L AC dosage, 40 °C and 150 rpm agitation speed. The highest 5-hydroxymethylfurfural removal efficiency was 92% at 7 g/L AC dosage. The adsorption data fitted best with the Langmuir isotherm model with a maximum uptake capacity of 70.92 mg/g (R2: 0.96). The zero-order reaction kinetic model was the most suitable one among the others inspected. It was determined that intraparticle diffusion was not the rate-limiting step. This study showed that waste hand paper hydrolysate can effectively be detoxified by activated carbon adsorption.