To demonstrate the availability of the water extraction-TBA (2-thiobarbituric acid) method, which had been improved by us for a test of fats deterioration, the reaction products in this method were analyzed by spectrophotometry and high performance liquid chromatography (HPLC). A red pigment with absorption maximum at 532 nm was formed by a reaction of malondialdehyde with TBA, which eluted at 5.6 min on the HPLC chromatogram. The reaction mixture of TBA and water extract from oxidized linoleic acid showed three absorption maxima at 450 nm, 495 nm and 532 nm. The HPLC could separate three reaction products into yellow (P-I), orange (P-II) and red pigments (P-III) with retention times at 2.3 min, 3.4 min and 5.6 min, respectively. The P-III was identical with the malondialdehyde-TBA adduct. P-I, P-II and P-III were also detected in the TBA test of water extracts from other rancidified fats (shark oil and soybean oil), as well as from oxidized linoleic acid. The TBA values obtained by the water extraction-TBA method with spectrophotometric detection corresponded well to those determined by the HPLC method in which the malondialdehyde-TBA adduct (P-III) was analyzed. Present results further demonstrated the availability of water extraction-TBA method as a convenient test for the determination of fats deterioration.