Waste cooking oil (WCO) biodiesel has some disadvantages, such as poor cold flow properties, low oxidation stability, and flash point during storage. These poor physicochemical properties can be improved by different ways, such as the addition of non-edible oil. The aim of this study to analyse physicochemical properties of the biodiesel made by between WCO and Schleichera oleosa (SO). The biodiesel produced with 70:30% of WCO and SO respectively as crude oil, further introducing of different KOH-based catalyst into this oil to obtained the methyl ester. The optimum yield transesterification process are 94% with 60 min. of the reaction time, 1 wt.% KOH, and 12:1 molar ratio the methanol to oil. On the other hand, the Schleichera oleosa blend shows oxidation stability at 6.8 h and 3.3 h for Waste cooking oil methyl ester (WCME). The reduction of cold flow and, on the contrary, the flash point increase were obtained with a 70:30% ratio of WCO and SO. The cold flow properties and flash point of the fuel. Thus, mixed WCO and Schleichera oleosa oil improve the physiochemical properties such as oxidation stability, flash point, and cold flow of biodiesel without the need for synthetic antioxidants.