In this study, the effect of chitosan alkali treatment supported onto agave fiber‐high density polyethylene composites over their Pb(II) adsorption properties was evaluated. The chitosan was placed in a beaker with a solution of NaOH bubbling air for 24 hours and controlling the pH around 10. Afterwards the chitosan was washed, filtered and dried. Composite pellets with 30% of agave fibers and 70% of high density polyethylene (HDPE) were coated with untreated chitosan (UC) and treated chitosan (TC) to be used in batch Pb(II) adsorption experiments. The results showed that the adsorption process was described by the Langmuir behavior and with a pseudo second order kinetics for both, UC and TC composites. The maximum adsorption capacities were obtained at pH = 5 with values of 2.08 and 2.44 mg/g composite for UC and TC composites respectively which represents an improvement of 17% by the alkali treatment. FTIR and NMR analysis were also carried out for a better understanding of the adsorption process.