In this experiment, we studied the effects of fattening periods (at 19, 24, and 29 months of age) on the expression of the C/EBP family (C/EBP alpha, C/EBP beta, and C/EBP delta) and PPAR gamma protein levels by Western blot analysis from different fat depots (subcutaneous, intermuscular, and mesenteric fat tissue) of Japanese Black steers. The expressions of C/EBP beta-liver-enriched activator protein (LAP), which activates preadipocyte differentiation, in subcutaneous, intermuscular, and mesenteric fat tissue at 29 months of age were significantly lower than those at 19 months. On the other hand, the expressions of C/EBP beta-liver-enriched inhibitory protein (LIP), which represses preadipocyte differentiation, in subcutaneous and intermuscular fat tissue in 29 months of age were significantly higher than those at 19 months. The expressions of C/EBP alpha, which activates adipocyte terminal differentiation, in intermuscular fat tissue at 29 months of age were significantly higher than those at 19 months. No significant differences in the C/EBP delta and PPAR gamma levels were observed in the fattening periods for any fat depots. These results suggest that adipogenic transcription factors, especially C/EBP beta and C/EBP alpha, play an important role in regulating adipogenesis during the fattening periods of Japanese Black cattle. (c) 2006 Elsevier Ltd. All rights reserved.