This study focuses on the introduction of a new biodiesel resource, Kachnar seed oil (KSO). The raw oil was extracted from the seed by Soxhlet extraction. The composition of fatty acids and physicochemical properties of the raw oil were measured. Methyl ester was produced from the raw Kachnar seed oil using a transesterification process using an alkaline catalyst. The new biodiesel, Kachnar methyl ester (KME), meets biodiesel standards and could be a reliable substitute for diesel in diesel engine applications. This paper also investigates a methodology to improve the oxidation stability of Kachnar biodiesel by blending it with diesel and by using different commercially available antioxidants, namely butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA), propyl gallate (PG), and pyrogallol (PY), in the produced biodiesel. The antioxidants were dosed in concentrations ranging from 100 to 1,000 parts per million (ppm). The result of the investigation shows that antioxidants PY and PG demonstrated effective results for improving oxidation stability of Kachnar biodiesel. TBHQ was the least effective among the investigated antioxidants, whereas the KME10 blend can maintain its stability without any antioxidant.