An attempt has been made to characterize the field-induced needle-like structures (secondary cluster SC) in ionic and water-based magnetic fluids (MFs) using Rayleigh light scattering technique. This technique has the advantage of detecting objects smaller than the resolution limit of the optical column. From the observations, it was found that though water is the solvent in both ionic and water-based magnetic fluids, the cluster characteristics under zero and applied magnetic field, their growth and disintegration were different.