Natural organic matter (NOM) consists of natural charged macromolecules and are ubiquitous in the aquatic environment. NOM can be adsorbed onto the surface of colloidal particles transporting through porous media. The adsorbed layers of charged macromolecules can provide additional electrosteric repulsions that enhance the migration of colloidal particles in the subsurface environment. Semi-empirical correlations for predicting the collision efficiency of electrostatically stabilized (bare) colloids have been proposed by Elimelech (1992) and Bai and Tien (1999), but their validity for predicting the collision efficiency of colloids coated with NOM has not been evaluated. In this study, we evaluate the predictive ability of these available correlations and demonstrate that adsorbed NOM layer properties have a strong influence on the deposition of NOM coated particles. The correlations were therefore modified to predict the collision efficiency of colloids coated with NOM by taking the adsorbed layer properties into account. Existing data for collision efficiencies of colloids coated with various NOM were taken from the literature (Amirbahman and Olson 1993 and 1995; Franchi and O'Melia 2003) and re-evaluated. The existing semi-empirical approaches for predicting the collision efficiency of bare particles have been demonstrated to substantially overestimate the deposition of NOM coated particles for a factor of 4.3 to 966, presumably due to fundamental differences in the strength and range of electrosteric repulsions compared to standard electrostatic double layer repulsion. The adsorbed NOM layers on colloids were estimated from electrophoretic mobility data using Ohshima's soft particle theory. The adsorbed layer thicknesses (dM0) of humic acids are thicker than those of the fulvic acids for a given particle type. To update the correlations, a steric repulsion parameter (NSTR) representing steric repulsion from adsorbed NOM layers is added to the set of four dimensionless parameters (NLo, NE1, NE2, and NDL) governing the collision efficiency of charge stabilized particles originally suggested by Bai and Tien. NSTR involves the adsorbed NOM layer thickness obtained form Ohshima's model and the adsorbed mass of NOM on the surface of colloidal particles. Partial regression analysis has been conducted and suggested the importance of NSTR on the deposition of colloids coated with NOM. The modified correlation provides greater predictive ability for NOM-coaed particle collision efficiencies. This study emphasizes the importance of characterizing the adsorbed NOM layer properties for the prediction of collision efficiency in porous media.