The prevalence of diabetes mellitus has increased tremendously in developing countries of tropical regions. The need for an effective and safe alternative is of importance as oral hypoglycaemic drugs have reported to cause side effects on prolonged use. In the present study two tropical plants, Hibiscus sabdariffa calyx and Stevia rebaudiana leaves were assessed for their in vitro antioxidant and antidiabetic activities. Total phenol and flavonoids of ethanolic extracts were quantified. Bioactive compounds were screened by Gas Chromatography Mass Spectrometry (GC-MS) analysis. Antioxidant activity was assessed by 1,1-Diphenyl-2-picryl-hydrazyl (DPPH) and superoxide radical scavenging assays. Antidiabetic ability was evaluated by inhibition of enzymes involved in carbohydrate metabolism. Glucose uptake by 3T3-L1 cells was also assessed. Ethanolic extract of Stevia leaf (EtSL) had a higher percentage of phenol and flavonoids. The GCMS analysis showed the presence of phytochemicals like Phenol-2,4-bis (1,1-dimethylethyl) in Roselle calyx and 6-methoxyflavone in Stevia leaves. The antioxidant assessment showed that EtSL significantly inhibited superoxide radical (IC50=45.81±1.21 μg/mL). The antidiabetic assessment revealed that Ethanolic extract of Roselle calyx (EtRC) showed strong inhibition of alpha amylase (IC50=27.95±0.32 μg/mL) and alpha glucosidase (IC50=6.21±0.18 μg/mL). Glucose uptake in 3T3-L1 cells demonstrated that both plants had significant insulin sensitizing ability. It was also revealed that the phenol and flavonoid content strongly correlated with IC50 values of antioxidant and antidiabetic assays. Results of this study show that both plants are a potential source of bioactive phytochemicals and can be used as a plant-based antioxidant and antidiabetic agent.