Detailed studies including synthesis, characterization and evaluation of antimony thioantimonate, SbSbS1, have been carried out. The amorphorus complex chalcogenide was prepared by a solution precipitation method. As a solid-lubricant additive in various greases, this material exhibits superior extreme-pressure and antiwear properties as demonstrated by the Four-Ball weld points and load-wear indexes on both AISI-52100 and AISI-440C steels. Antimony thioantimonate appears to be compatible with all the base greases investigated including a silicone grease in which very few additives show good response.Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.