Background Averrhoa carambola fruit is consumed by many people because of its sweetness and medicinal values. However, there is a dearth of researched information on its complete toxicity profile. This study investigated the possible toxicity potentials of star fruit juice in female albino rats. Methods Thirty-five rats assigned into seven groups of five rats each and administered with varying doses (0, 250, 500, 1000, 2000, 4000 and 5000 mg/kg) of the juice were used for acute toxicity studies. Another 20 rats assigned to four groups (A-D) of five rats each were administered the juice at 0, 600, 400 and 200 mg/kg body weight orally for 28 days. On the 29th day, whole blood, sera and vital organs were collected for hematological, serum biochemical and histopathological analyses, respectively. Results Acute study results indicate that the juice was safe even at 5000 mg/kg after 48 h. In the subacute studies, there were no significant (p < 0.05) differences in all hematological parameters, total protein, albumin and globulin values of the treated groups compared with those of the control group. The aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase activities, as well as urea, creatinine and malondialdehyde values of the rats treated with the juice were significantly (p < 0.05) higher than those of the control rats in a dose-dependent manner. The liver and kidney histomorphologies of the rats treated with the juice showed lesions of degeneration and necrosis when compared with those of the control. Conclusion The juice of A. carambola is both nephrotoxic and hepatotoxic but had no deleterious effects on the hematology.