Global demand for industrial lubricants is increasing every year in line with the increasing of production and demand of various products. Castor oil has been acknowledged as one of vegetable oil base lubricant source that has advantages over mineral based lubricants due to their renewability properties. However, the use of this oil as industrial for long period of time is considered limited due to its tendency to oxidation which may lead to formation of deposition and varnish. Butylated hydroxytoluene (BHT) and tert-Butylhydroquinone (tBHQ) are typical additives added to various food grade vegetable oils and animal fats to enhance their preservation time. This research is carried out to: (i) examine the oxidation prevention properties bht and tbhq additives to castor oil due to high temperature, (ii) examine the effect of BHT and tBHQ loading to viscosity index of castor oil. Commercially available Castor oil was employed as base oil. The oil was loaded with 2.5–10 wt.% of BHT and tBHQ additives respectively. The oxidation of the oil was examined by adopting IP-48 standard testing. In this test, air was bubbled at 15 l/h of flow rate during a period of 6 h throughout 40 ml of oil sample at 150 ℃. The oxidation prevention effect was determined from viscosity changes of the oil before and after testing at two temperatures of 40 ℃ and 100 ℃ respectively. The viscosity test was in accordance with the ASTM D445 and the viscosity index was calculated by ASTM D2270 standard method. The results shows BHT additive has better oxidation prevention compared to tBHQ additive. Optimum BHT loading is found at 2.5 wt.% and optimum tBHQ loading is at 5 wt.%. Oxidation process was found to have reduced the VI value although not so significant.