The release and uptake of the Zinc (Zn+2), being the important micronutrient element in soil, is often regulated by the humic/fulvic substances present in the soil. Zinc forms stable complexes with soil organic matter, where humic acid (HA) and fulvic acid (FA) fractions play an important role for the adsorption processes. However, the stability of the organo-zinc complexes signifies the intricacy of the organo-zinc dynamics in soil. The soils under study were neutral to acidic in nature with high organic carbon content, having wide variations in the extractable phosphorus and other exchangeable cations. The DTPA-extractable Zn was found to be low on the basis of its critical limit in soils, of these areas. The stability constant (logK) of the complexes, formed by the natural humic/fulvic acids with Zn in aqueous phase, was evaluated by the Ion-exchange method. Results tend to suggest that the given organo-zinc complexes were quite stable as evaluated with the corresponding logK values of the humic/fulvic acid samples. This depends on the nature and properties of the humic polymer, which in turn, would affect the retention/release of such element (Zn) in soil-plant systems.