The lubricating oil or oil used for motorbikes currently has a lot of variety, from lubricating oils made from minerals, semi-synthetic and synthetic, synthetic based lubricating oils have been known to have better quality than mineral and semi-synthetic lubricating oils. . But synthetic lubricating oil with high quality / price is not necessarily suitable for the needs of all motorbikes, there were times when the motorcycle actually got the best performance in mineral or semisynthetic lubricating oils. Therefore it is necessary to know the characteristics of each lubricating oil in order to know which lubricating oil is good and suitable for each motorcycle engine. The study this time examined to determine the effect of viscosity characteristics and thermal conductivity of several types of lubricating oils with SAE 10W-40 and SAE 20W-50 on the performance of Honda GL GL 145cc motorcycles in 1987. By using 3 synthetic lubricating oils namely Prima XP, Fastron Techno and Castrol Magnatec compared to standard mineral type lubricants, namely Super Mesran. Test methods include measuring thermal conductivity, viscosity, torque, power, working temperature and fuel consumption. For the fuel used is the RON 90 Pertalite using a Honda GL PRO 145cc motorbike traveling a distance of 4 km at an average speed of 40 km / hour. The results of the research showed that the highest viscosity of the Mesran Super oil while the thermal conductivity of lubricating oil was the highest. The maximum torque value which is affected by Mesran Super lubricating oil is 10.57 N.m, Prima XP lubricating oil of 10.38 N.m, Fastron Techno lubricant oil of 9.68 N.m, and Castrol Magnatec lubricating oil of 11.46 N.m. For maximum power values affected by Mesran Super lubricating oil of 12.1 HP, Prima XP lubricating oil of 12 HP, Fastron Techno lubricating oil of 11.9 HP, and Castrol Magnatec lubricating oil of 10.8 HP. The consumption of Mesran Super lubricant fuel has a distance effect for each liter of fuel as far as 48.72 km / liter, Prima XP lubricating oil as much as 48.97 km / liter, Fastron Techno lubricant oil as far as 47.50 km / liter, and lubricating oil Castrol Magnatec is 46.02 km / liter. It can be concluded from the data obtained from the test that it proves that synthetic lubricating oil is better because synthetic lubricating oil has an addictive substance that can improve the function of lubricating oil when operating compared to mineral lubricating oil.