Sahara myrtle is a Myrtaceae indigenous plant, widely found in central Sahara of Algeria, used for diabetes treatment. In the present study, the chemical content, hypoglycaemic and antioxidant potential of Myrtus nivellei decoction were evaluated by using in vitro, and in vivo methods. After the oral administration of decoction at doses of 100 mg/kg and 300 mg/kg, body weight, blood glucose levels and some biochemical parameters were monitored at specific intervals. Glibenclamide was used as a reference drug at a dose of 5 mg/kg. The experimental data indicated that the decoction of Sahara myrtle demonstrated significant antihyperglycaemic effect in alloxanic rats especially at a dose of 300 mg/kg which confirmed the folkloric utilization. Phenolic, total tannin and flavonoid contents of extract were also determined in this order: 204,67±1.87 µg and 190,62±1,11µg (gallic acid equivalent/mg extract) and total flavanoids 85,32±13,67µg (rutin equivalent/mg extract). It was concluded that this antidiabetic activity of Myrtus nivellei was probably, due to its high phenolic, total tannin, flavonoid contents and antioxidant effects.