Abstract: The present study evaluates the efficiency of conversion of CLNA (conjugated linolenic acids; α-eleostearic acid) of Ricinodendron heudelotii to CLA (conjugated linoleic acids; rumenic acid) in the liver, small bowel and serum of male rats using ultraviolet spectrometry (UV) and Gas Chromatography (GC) techniques. One milliliter of oil was orally administrated to 30 rats during 24 h. The spectra of R. heudelotii oil, linoleic acid, rumenic acid and α-eleostearic acid (α-ESA) were determined. The concentrations of α-ESA and CLA were determined after 0, 3, 6, 12 and 24 h of oral administration of oil in liver, small bowel and serum. Linoleic acid has a peak at 215 nm and rumenic acid at 232 nm. Spectra of standard α-eleostearic acid and R. heudelotii oil were bunk with a characteristic peak at 270 nm. In the serum, we did not find any trace of fatty acid with either UV or GC. UV and GC methods showed that α-ESA was gradually converted in rumenic acid in the liver and small bowel. The liver had a faster and higher enzyme activity than the small bowel. These results showed that the conversion of CLNA to CLA in rats using UV spectrometry is the most method to use.