An agricultural tractor is a machine that performs many operations, such as land preparation, cultivation, towing and PTO operation, to name a few. In Japan it must operate in a wide variety of agricultural applications, such as paddy farming, upland farming, fruit farming and dairy farming, and in all kinds of weather. The recent trend has been toward higher-powered tractors to increase working efficiency, and automated transmission and hydro-electronic controlled mechanisms to promote improved operability, comfort and other amenities. With a dramatic advance of such technology, it was of urgent necessity to improve even more the low-temperature fluidity, friction characteristics and extreme-pressure performance of the lubricating oil. In recent years, as the environmental pollution problem arises, there is an increasing need for biodegradable lubricating oil.Tractor lubricating oil is a multipurpose oil that performs duties such as hydraulic control that operate the three-point link mechanism, hydrostatic transmission (HST), power shift transmission including gears, bearings and wet clutch, power steering, and wet disc brakes. To exhibit their performance efficiently with the same type of oil, the characteristics of the lubricating oil must be improved even more (Table 1). In recent years, as the hydraulic control mechanism advances, the demand for performance improvements with emphasis on low-temperature fluidity and improved friction characteristics has been increasing.Taking a worldwide look at the agricultural tractor market, the conditions fall roughly into two categories: damp regions (humid regions) such as what is found in Southeast Asia and dry and irrigated farming (semiarid regions) such as America and Europe. The problem in the high humid regions is that the moisture entering through the air breather is condensed, when the tractor is not used for a long period of time. With repeated changes in temperature, water enters the transmission case of the tractor. The tractor generally has a life-span of 10 or more years. There is a limited usage within a given year depending on the regions where the tractor is used. It may be left unused for several months at a time. Under these conditions, lubricating oil is required to prevent the performance of the tractor from deteriorating.While maintaining and improving the performance of the lubricating oil on the basis of specific operating conditions, Kubota has established its own required performance of and the method for test evaluation of the lubricating oil. It has developed a new dual-purpose transmission and hydraulic lubricating oil, Kubota Super UDT (Universal Dynamic Tractor Oil). It replaces conventional lubricating oil (Kubota UDT). Kubota, in cooperation with lubricating oil manufacturers has developed “Bio-Super” UDT with an additional feature of Biodegradability to Super UDT (only in Japan). This paper deals with Kubota's own performance requirements and method for test evaluation of the lubricating oil.