Arsenic (As) contamination of soil, surface water and groundwater is widespread in the world due to mining exploitation and hydrogeological occurrence. Arsenic mobility increased in liquid phase due to association with FH_C through formation of inner-sphere complexation. Moreover, dissolved organic matter (DOM) or organic colloids regulate the transport and fate of colloid and colloid-associated contaminants. Humic acid (HA), the most representative organic matter in soils, are important in controlling the distance of FH_C transport and deposition position in porous media. However, little is known about effects of humic acid colloid (HA_C) and FH_C interaction on transport and deposition of As in porous media. Co-transport of HA_C-FH_C and As at different pH was systematically investigated by monitoring breakthrough curves (BTCs) in saturated sand columns. Colloid and solute transport models were used to reveal mechanisms of As transport with HA_C-FH_C in porous media. Our data indicated that the interaction between HA_C and FH_C highly influenced the fate of FH_C-associated As. Although HA_C with high concentrations enhanced FH_C transport and further facilitated transport of FH_C-associated As, an excess of HA_C occupied the adsorption sites of FH_C and thus decreased As co-transport with the mixed HA_C-FH_C colloids. Humic acid colloid-enhanced FH_C transport and As adsorption on the mixed colloids were controlled by environmental pH. Although, under the alkaline condition, HA_C significantly enhanced FH_C and As transport, more As was adsorbed on the mixed colloid and co-transported under slightly alkaline or neutral pH conditions when chain-shaped HA_C was present. With decreasing pH, As was gradually co-deposited with FH_C since HA_C was transformed to sphere-shaped one. The fate of As changed from co-transport with HA_C-FH_C to co-deposition when environmental pH further decreased. Future research should focus on applying surface complexation models, such as charge distribution multisite surface complexation (CD-MUSIC) and ligand charge distribution (LCD) models, and reactive transport models to quantify colloid-facilitated transport of contaminants in order to understand the micro-interfacial process and co-transport mechanisms of colloids and contaminants.