The effects of supplementing diets with a mixture of conjugated linoleic acid (CLA) isomers (CLAmix) and/or selenium as Na₂SeO₃ (SeIV) or selenized yeast (SeY) on the growth performance of rats and on the contents of some fatty acids (FA) in their abdominal fat and brains were investigated. The study was performed on 80 female Wistar rats (Hsd Brl Han: WIST), 8 weeks of age with an initial body weight of 195.4±0.8 g. Each group numbered 8 rats. During the 7-day preliminary period the rats were fed a standard Labofeed H diet at a sub-maintenance level. Next, for 6 weeks the rats were fed ad libitum on the experimental diets supplemented with CLAmix, 0.2 ppm Se or 0.5 ppm Se as SeIV (_LSeIV or _HSeIV, respectively) and SeY (_LSeY or _HSeY, respectively). The rats were sacrificed at the end of the six-week experimental period. The diets enriched in _HSeIV, _LSeY, or _HSeY increased the body weight gain (BWG) compared with the control rats, while the dietary CLAmix had a negligible effect on BWG in comparison with the control group. The addition of CLAmix to the diet enriched in Se, regardless of the level of extra Se and its chemical form, showed a negligible influence on the BWG in animals compared with rats fed the diet containing only _LSeIV, _HSeIV, _LSeY or _HSeY, respectively. Dietary _LSeIV resulted in a decrease in the content of saturated fatty acids (SFA), atherogenic SFA (A-SFA), thrombogenic SFA (T-SFA), mono- (MUFA), poly- (PUFA) unsaturated fatty acids, PUFAn-3, PUFAn-6, c9C18:1, c9c12C18:2 (LA), c6c9c12C18:3 γ-LNA), c9c12c15C18:3 (α-LNA) and the sum of FA in the fat of rats. The diets enriched in CLAmix, _HSeIV, _LSeY or _HSeY generally exhibited a smaller influence on the level of these FA in the fat compared with rats fed the diet with _LSeIV. The diet with _LSeIV had a negligible influence on the content of long-chain PUFAn-3 and n-6 (LPUFAn-3 and LPUFAn-6) in the fat compared with the control rats. The diet with _LSeIV numerically or statistically increased the ratio of PUFA/SFA, MUFA/SFA, UFA/SFA, and PUFA/FA in the fat compared with the control group. Other experimental diets resulted in inconsistent and negligible changes of these ratios in the fat compared with the control group. The diets with CLAmix or Se (as SeIV or SeY) reduced the content of C14:0, C16:0, C18:0, c9C18:1, LA, αLNA, c11c14c17C20:3, c8c11c14C20:3, c5c8c11c14C20:4, c7c10c13c16c19C22:5, c4c7c10c13c16 c19C22:6, SFA, A-SFA, T-SFA, MUFA, PUFAn-3, LPUFAn-3, PUFAn-6 and LPUFAn-6 in the brain compared with the control group. The diet enriched in CLAmix and Se (as _LSeIV, _HSeIV, _LSeY or _HSeY) decreased the content of these FA in the brain (the interactions: P<0.01). The ratio of PUFA/SFA, MUFA/SFA, UFA/FA and PUFA/FA was higher (P<0.01) in the brain of rats fed the diet with the one additive than in the control group. The diet enriched in CLAmix or Se (as SeIV or SeY) decreased Δ9-desaturase capacity in comparison with the control rats; interaction effects of CLAmix x Se (as _HSeIV, _LSeY or _HSeY) were found (P<0.01). Feeding rats with the diet enriched in _HSeIV or _HSeY with or without CLAmix improved the nutritive value of the abdominal fat by increasing the content of LPUFAn-3, while the PUFAn-6/PUFAn-3 ratio decreased, particularly in the fat of rats fed the diet containing SeY. Finding that diets enriched in CLAmix and _LSeY or _HSeIV most effectively increased the content of CLA isomers in the abdominal fat and efficiently elevated body weight accretion and feed conversion efficiency in rats is valuable information for nutritionists carrying out research to improve the value of food derived from monogastric animals for human health.