The imbalance between promoters and inhibitors in the kidneys leads to Kidney stone formation or urolithiasis. The effects of aqueous and ethyl acetate extracts of Ferula communis L(Fc) and Verbena officinalis L (Vo), on the growth rate of COM crystals, were studied by using a constant composition technique in the absence and presence of inhibitors over the range of relative supersaturation (σ=0.23–0.70). The effect of I, pH, T, and size of particle seed crystal parameters was evaluated. Our results reveal that the aqueous extracts of Fc and Vo were found more effective than ethyl acetate extracts on crystal growth of CaOx.H₂O experimentally, with the highest inhibition at 86.7% of aqueous (Fc) compare to 80.70 % for aqueous (Vo) in compare with 71.56% and 62.39% for ethyl acetate (Fc) and ethyl acetate (Vo) respectively at the same concentration and the same relative supersaturation degree. The dependence of the rates of COM crystallization in the presence of inhibitors was found to be second order suggesting a surface-controlled mechanism with n ≈ 2, these results were supported by the low value of activation energy Ea=5.004 kcal. The adsorption of the additive on the crystal surface can be interpreted in term of Langmuir adsorption isotherm, and K_L values determined in the presence of Aqua. (Fc), Aqua (Vo), Ethyl. acetate.((Fc)and Ethyl acetate (Vo) were 7.31 x10⁵, 4.7x 10⁵, 3.06x 10⁵, 1.6 x 10⁵ J/mol respectively indicating potent inhibitory influenced of these plant extracts.