Waste fat is an integral part of the processing of animal by-products in rendering plants. The flow behav- ior and time-dependent flow properties of waste fat in the temperature range of 10ºC, 20ºC, 30ºC, and 62ºC was studied. Waste fat presented non-Newtonian behavior. Three mathematical models were used for predic- tion of the flow behavior of waste fat, including the Casson, Steiger-Ory, and Herschel-Bulkley models. The Herschel-Bulkley model sufficiently described the flow behavior of the waste fat at different temperatures. Several kinds of rheological curves were determinated for description of the flow behavior. Rheopectic behav- ior of rendered fat was determinated at temperatures lower than 30ºC.