The influence of resins on asphaltene aggregation is studied using a molecular thermodynamic approach. The formation of mixed resin-asphaltene aggregates is described using a model previously developed for asphaltene aggregates. In this model, the aggregates are described as aromatic cores composed of stacked aromatic sheets surrounded by aliphatic chains. Using this simple description for the aggregates, an analytical expression is developed for the free energy of mixed aggregation. This expression incorporates solubility, mixing, and interfacial and steric effects. The proposed model predicts that the presence of resins decreases the size of the aggregates and also increases the cmc of the asphaltene solutions in agreement with the experimental observed behavior. The effectiveness of different resins to split the asphaltene aggregates depends upon the solubility of their polyaromatic ring. The lower the solubility, the larger the effectiveness of the resins because more resins are able to be incorporated inside the aggregates. In addition, the thermodynamic molecular model developed does not use any information derived from experiments on asphaltene/resin solutions, and therefore, it is strictly predictive.