There are many natural remedies derived from herbs have been used as alternatives to treat kidney stones disease effectively including Euphorbia hirta L. and Orthosiphon stamineus. Therefore, the present study aims to investigate the effect of four different extraction solvents of E. hirta and O. stamineus including hexane, methanol, ethyl acetate and water to inhibit the crystallization of calcium oxalate (CaOx) in-vitro. The inhibition of crystallization was studied by using rate of CaOx aggregation assay and was determined by UV-Vis spectrophotometer. Cystone was used as positive control. The result showed the best inhibition in aggregation of CaOx was exhibited by hexane extract of E. hirta (95.78%) which had no significant difference with Cystone, and the lowest inhibition was shown by hexane extract of O. stamineus (20%±). It could be related to the presence of higher amount of alkaloid in hexane extract of E. hirta as compared to other extracts. In conclusion, both of plant extracts showed antiurolithiatic properties by inhibiting the crystallization of calcium oxalate. However, the rate of inhibition for both plants varies depending on the type of solvent used.