The antioxidant and antihyperlipidaemic activities of P. guajava and R. americanum leaves aqueous extract were studied using in vitro and in vivo experimental models. The free radical scavenging activity, lipid peroxide inhibitory effects in RBC ghost and liver homogenate lipids, effects on viability and cytotoxicity of oxidant challenged S. cerevisae and effects on rats fed on high fat feeds and salted water were studied. Sequential fractionation of the aqueous extract with hexane, methylene chloride, ethylacetate, methanol and subsequent antioxidant and antihyperlipidaemic activity of the fractions was carried out. Further fractionation of the methanol fraction of R. americanum aqueous leaves extract using column chromatography and bioassay of the fractions was undertaken. FTIR and GCMS analysis of the active fractions and subsequent identification of the active components of the fractions was also carried out. This study showed P. guajava and R. americanum leaves posses significant antioxidant and antihyperlipidaemic activity. The study also showed the leaves' Cyanidin has the antilipidaemic activity while cyanidin, kaemferol and quercetin contribute to the antioxidant activity