Two orange (Citrus sinensis) fruit varieties, Navel and Valencia, from Muheza in Tanga, were analyzed for their proximate composition (ash, acidity, crude fat, crude fibre, sugars and moisture content), ascorbic acid, sugars, concentrations of four macro elements (Ca, Mg, K, Na) and seven heavy metals (Al, Cd, Cu, Fe, Mn, Pb, Zn). The oranges had high moisture content (>68%), moderate titratable acidity (0.60 – 1.65% c.a.), low crude fat content (0.60 – 0.66 g/100 g-fresh weight (fw)), low crude fibre amounts (0.63 – 0.75 g/100 g-fw), low ash content (0.68 – 0.72 g/100 g-fw), high reducing sugars (6.6 – 13.1%), high total sugars (11.4 – 33.4%), high total soluble solids (11.5 – 31.8%) and high ascorbic acid (22.5 – 50.4%). Very low concentrations of the seven heavy metals were detected in the fruits. Ascorbic acid, moisture, titratable acidity, sugars content varied within the season and with storage-ripening time. The high moisture content suggests the usefulness of these fruits in the treatment of obesity. The citric acid which these fruits contain makes them to be used as acid foods when required. The value of ascorbic acid which is above 30 mg/day in these fruits allows them to be considered as good sources of ascorbic acid for human nutrition.