The present study aimed at evaluating the effects of domestic culinary treatment on phytochemical contents (phenolic content and dietary fiber), and the antidiabetic potential of Vernonia amygdalina in type 2 diabetic rats. The culinary forms implied boiling leaves of V. amygdalina directly and eliminating the leaves’ bitterness before boiling. Seventy wistar rats were artificially induced with type 2 diabetes using streptozotocin and high‐fat diet. They then received by oral intubation powders of different culinary forms of leaves extract or suspensions of V. amygdalina at a dose of 500 mg /kg for a period of 4 weeks. The crude fiber, total phenol contents and the DPPH scavenging ability of these culinary forms were also measured and the results showed that values of these parameters were higher in the unwashed form than the washed form. The washed and unwashed forms of V. amygdalina significantly reduced ( p < 0.05) the blood glucose, the total cholesterol, triglyceride, transaminases, urea and creatine levels. Aqueous extract has the highest ability to reduce the blood glucose level (75.76%) followed by the unwashed form (61.17%) which was greater than that of the washed form. Also, these forms significantly increased serum HDL cholesterol and total protein level, with the highest activity obtained with the unwashed form. Washing the V. amygdalina leaves (that consists of multiple trituration of leaves with water) contributes to the reduction of antidiabetic and antioxidant properties.