In this study the behavior of nano magnetite colloid particles with polystyrene coated in the presence of an external magnetic field was investigated. It is observed that the average cluster size and the number of clusters show a power law behavior with time, both in aggregation and disaggregation processes. Adding sodium dodecyl sulfate (SDS) change during coated process the value of z and z’, the dynamical exponents’ of power law, and has optimum value. At this value the aggregation and disaggregation exponents are almost equal, z~z
