In situ image analyzing measurements are applied in determining the evolution of crude oil asphaltene aggregate size distribution in toluene solutions, The experimental data are compared to the predictions of a population balance model. The effect of different asphaltenes nature on the fractal-like aggregate size is investigated as a function of shear rate and toluene to n-heptane volume ratio. Good agreement is found for the average size evolution of asphaltene aggregate size distribution, assuming a fractal approach for model discretization. Initially, the average-number asphaltene aggregate size increases with time and then beyond a maximum value decreases to an almost constant steady-state size. The aggregates fractal dimension value can strongly affect the evolution kinetics of aggregation.