Colloidal humic acid (HA) acts as a vector that can facilitate the transport of contaminants in groundwater. However, investigations of factors that enhance the transport of sulfa antibiotics when there are colloids present remain incomplete to date. In this study, column experiments were performed under different conditions (particle size, pH, ionic strength, cation valence, colloidal concentration) using 0.25 mg/L sulfamerazine (SM) with or without colloids. The results showed that antibiotics were more easily deposited on the surface of porous media with a diameter of 0.22 mm than 0.45 mm. As the pH increased from 6 to 8, adding colloidal HA increased the maximum breakthrough concentration from 0.94 to 1 for SM. Adding colloidal HA at different NaCl concentrations decreased the maximum C/C0 ratio from 0.97 to 0.92. However, adding colloidal HA changed the C/C0 ratio more when the divalent cation (Ca2+) was present. Overall, increasing the colloidal HA concentration clearly caused the effluent sulfamerazine concentration to increase.