Abstract: A comparison between six different types of linear expression of the widely usedpseudo-second-order kinetic model, for the adsorptionofmethylene blueon hydrochloric acid-treated rice huskwas made. The results showed that it was inappropriate to use the type 1 expression of pseudo-second-order equation to calculate the pseudo-second-order rate constantsand to predict qt for the studied system, even the type 1 expression had high R2 value. The modeling of kinetic results showed that the studied system (methylene blue/hydrochloric acid-treated rice husk) was best described by the type 6 expressionof the pseudo-second-order equation