The growth process of large fractal aggregates formed by diffusion and rotation of silver clusters on sillicone oil surfaces in investigated. Our results indicate that the silver clusters rotate randomly on the liquid substrates and the mean square angle displacement 2> and time difference Δt satisfy the generalized Einstein relation 2>=4DθΔt. The random rotation coefficient Dθ scales with the cluster size S as Dθ∝S－γθ, where γθ＝2.4±0.3. The dependence of the fractal dimension of the aggregates on the deposition rate and aggregate time is also presented.