Resumo. Abstract Aim The aim of this study was to evaluate the performance of the coagulant Polyaluminium chloride (PAC) in water quality improvement of six eutrophic shallow lakes in Brazilian semiarid region. Methods We evaluated the effect of PAC in turbidity, humic substances (UV254), total phosphorus and chlorophyll-a concentration through laboratory jar tests. Results The results showed that PAC had a good performance in reducing total phosphorus concentrations and turbidity, with a reduced efficiency in removing chlorophyll-a and humic substances by sedimentation of flocks formed. Conclusions Addition of PAC is a potential tool for water quality improvement of eutrophic shallow lakes in Brazilian semiarid region but its efficiency depends on the pH and particulate and dissolved organic matter concentration in the lake or reservoir water.