The aim of this study was to examine the effects of the hypolipemic drug fenofibrate (FF) and aging on the expression of factors/enzymes involved in brown adipose tissue (BAT) function and browning of white adipose tissue epididymal (eWAT) and subcutaneous (sWAT) depots. Young-adult and old male Wistar rats were fed standard chow (control) or supplemented with 0.1% or 0.5% FF for 30 days. Tissue samples were analysed for gene expression and protein content, and stained with Oil Red O or hematoxylin and eosin. In BAT of young rats, 0.5% FF increased only Cbp/p300 interacting transactivator with Glu/Asp rich carboxy-terminal domain 1 (CITED1) protein content and Fgf21 and Gpr109A mRNA expression. The expression of oxidative metabolism related genes (Pgc1α, Cpt1b, Mcad) decreased after 0.5% FF. In BAT of old rats, FF did not affect UCP1 and CITED1 content and had little effect on gene expression. Oil Red O staining of BAT revealed no changes in lipid droplet area upon treatment in either age group. In eWAT of young rats, 0.1FF elevated UCP1 protein content and Ucp1, Pgc-1α, and Mcad expression, whereas 0.5% FF increased PPARα content and Pgc-1α, Cpt1b, Mcad, and Gpr109A levels. In eWAT of old rats, only 0.1FF increased Pgc1α and Mcad expression. In both age groups median cell area of eWAT adipocytes was reduced after 0.5% FF. In sWAT Ucp1 gene expression was very low and UCP1 protein was undetectable. FF upregulated Ucp1, Cited1, Eva1, and Cpt1b expression in sWAT of young rats, with diminished effects in old rats. In both age groups 0.5% FF increased Fgf21 expression in sWAT. Median cell area of sWAT adipocytes decreased only in young rats treated with 0.5% FF. Our results reveal that fenofibrate differentially affects gene expression in BAT, with diminished effects in old compared to young rats. In WAT of young rats FF modestly stimulates the expression of factors/enzymes involved in lipid oxidative metabolism and browning. Aging reduces both these effects. Gpr109A may present a novel gene target upregulated by FF in BAT and eWAT.