Adsorptions of Cu on a Wushan soil colloid (WS) and a Red soil colloid (RS) with and without 2,4-D were studied by batch equilibrium experiments. The results indicated that Cu adsorption isotherms fit Langmuir equations well, with high correlation coefficient (R2 = 0.93 ~ 0.98). The WS had higher adsorption capacity for Cu than the RS. Cu adsorption quantities on the two soil colloids increased with the increase of solution pH values within the range from 3.0 to 6.7. The presence of 2,4-D increased Cu adsorption quantity on both of the soil colloids. The higher the solution 2,4-D concentration, the more Cu adsorbed on the soil colloids. It can be attributed to pH-increase induced by 2,4-D which resulted in the increase of the negative surface charges of soil colloids.