Uncaria guianensis (UG) and Uncaria tomentosa (UT) are widely found in the South America rainforest. Both species, popularly known as cat's claw, can be easily differentiated in natural state through their morphological characteristics. However, the discrimination of their derivatives, such as dried extracts, is limited to differences in their chemical composition. This work establishes differentiation criteria between both cat's claw species by multivariate analysis from FT-IR, UV, and LC-PDA data, as well as for adulteration recognition in UT stem bark. Eight authentic UT and UG stem bark samples and eighteen UT samples spiked with UG at three levels (10%, 30% and 50%, w/w) were extracted and analyzed by FT-IR analysis; direct UV analysis; UV analysis after basification and complexation with KOH and AlCl3, respectively; LC-PDA analysis of oxindole alkaloids, quinovic acid glycosides, and polyphenols. Classification (SIMCA and k-NN models) and calibration (PCR and PLS models) multivariate models were applied for adulteration recognition and quantification of their level, respectively. The authentic UT samples could not be differentiated those purposely spiked with UG from LC-PDA analysis of oxindole alkaloids. In contrast, LC-PDA analysis of polyphenols and UV analysis coupled to SIMCA and PLS multivariate models, allowed the differentiation between UT and UG and adulteration recognition in UT. Flavonoids were key compounds in both cases. Both UV and LC-PDA analysis of polyphenols coupled to multivariate analysis were effective for differentiation between cat's claw species, as well as adulteration recognition in the UT.