Both a Monte Carlo model and an algorithm were presented to simulate the particle coagulation and breakup phenomena taking place in a colloidal solution under turbulent fluid shear. The model is represented by the probability density functions that describe the stochastic coagulation and breakup phenomena taking place among numerous particles. From a dimensional analysis of the model two dimensionless groups, kc and kb, were derived that represent the relative intensity of the coagulation and breakup phenomena. In order to overcome the memory problem in saving the sizes of a large number of particles, the model was converted to a form suitable for carrying out a sectional mass balance. Detailed simulation steps were presented and applied to acrylonitrile-butadiene-styrene (ABS) latex coagulation. Numerical simulations revealed that the steady state particle size distribution does not depend on the initial distributions but on the kc/ kb ratio. Setting the operation variables to increase the ratio was found to shift the particle size distribution toward larger particles.