With increasing molybdenum ore mining, the difficult to treat ores, i.e., lower-grade and fine-disseminated ores have gradually increased in importance. Kerosene was widely used as the conventional collector of molybdenum flotation all along, but it does not adapt well to the flotation of molybdenite in difficult to treat ores. Meanwhile, kerosene has been cancelled from the manufacture catalogue in China, which makes large refineries no longer produce it, and in turn makes it difficult for a molybdenum flotation plant to purchase kerosene and makes it even harder for kerosene to keep a stable composition. Therefore, many molybdenum flotation plants began to apply diesel oil instead of kerosene as collector for molybdenite. However, the flotation results reveal that diesel oil from different manufacturers or being of different specifications from the same manufacturers has a different effect on the flotation of molybdenite, and pulp temperature has an obvious effect on the flotation efficiency of diesel oil. In pulp temperatures ranging from 10 to 30 degrees C, the flotation recovery of molybdenite increases with increasing high-boiling component in diesel oil. When pulp temperature is below 10 degrees C, the flotation recovery of molybdenite is related to the dispersibility of diesel oil, i.e., the proportion of high-boiling and low-boiling component in diesel oil. Therefore, a molybdenum flotation plant should not blindly apply diesel oil instead of kerosene as the collector for molybdenite, but should select diesel oil that is suitable for the properties of its ore. This technical note is helpful to better select the proper collector for a molybdenum flotation plant. (C) 2011 Elsevier Ltd. All rights reserved.