Phosphate adsorption capacities of palygorskites modified with acid varying in concentration in P-contaminated waters different in phosphate concentration were investigated. And effect of acid modification on the mechanism of palygorskite adsorbing phosphate was also studied through pH and zeta potential measurement. Results showed that acid modification to 3%～30% increased to a varying degree the phosphate adsorption capacity of natural palygorskite，which is actually unable to adsorb any phosphate. The effect of acid modification by 3% was the highest，enabling palygorskite，applied at a rate of 1%，remove 95% of the phosphate from water of Grade V (P 0.4 mg L^-1) and 15% from water of Grade Vminus (P 1.0 mg L^-1). Acid modification also influenced pH and zeta potential of palygorskite. The former decreased from 8.6 to 3.35，and the latter fluctuated with increasing acid concentration，and peaked up to about -28.1mV when palygorskite was acid-modified by 3%. The results depicted above reveal that acid modification changes surface charge and adsorption sites of palygorskite，thus enhancing its phosphate adsorption or removing capacity.