The reaction of 5-bromosalicylaldehyde with 1-mesityl-1-methyl-3-(2-chloro-1-oxoethyl)cyclobutane (1) and potassium carbonate was used to prepare (5-bromobenzofuran-2-yl)(3-methyl-3-mesitylcyclobutyl)methanone (2) for the starting reagent purposes. (5-Bromobenzofuran-2-yl)(3-methyl-3-mesitylcyclobutyl)ketonethiosemicarbazone (3) was synthesized from the reaction of the compound (2) with thiosemicarbazide. In the present study, it was aimed to examine the influence of synthetic (5-bromobenzofuran-2-yl)(3-methyl-3-mesityl cyclobutyl)ketonethiosemicarbazone on levels of vitamins (A, E, C), selenium and malondialdehyde in rats. A total of 42 rats were used and the animals were divided into two groups in the study. Only a subcutaneous injection of 250 microl of 75% ethanol was given to the control group every other day. A subcutaneous injection of this compound (25 mg kg-1, dissolved in 250 microl of 75% ethanol) was administered to the other group of rats. After the application of (5-bromobenzofuran-2-yl)(3-methyl-3-mesitylcyclobutyl)ketonethiosemicarbazone for 20 days, the serum vitamins (A, E, C) and malondialdehyde levels were determined with high performance liquid chromatography, the serum selenium level was determined by using fluorescence spectrophotometer. The serum vitamin A, E, C and selenium levels were significantly decreased compared to control group (P<0.005), whereas serum malondialdehyde levels were higher than control group levels (P<0.005). As a result, it could be suggested that this compound induced a severe stress, and also increased the amount of free radicals depending on the stress.