Phenobarbital is a phenobarbiturate used as a sedative, anticonvulsant or hypnotic with the doses prescribed and can cause teratogenic effects. The goal of this study was to examine an alternative method for the recognition of the mechanism or the bimolecular potential changes in mice fetus caused by Phenobarbital using FTIR micro spectroscopy. The mice were injected with Phenobarbital (120 mg/Kg) on gestation day 9. Fetuses were dissected on day 15 of gestation and morphological and histological studies on the fetus were carried out. Sections (10 μ m) of normal and Phenobarbital treated fetus brains and livers were used for FTIR measurement in the wave number region of 400-4000 cm. The results were shown by 2 derivatization of spectra and also subtracting from control spectra. In liver, the intensity at 1054 cm, 1155 cm, 1353 cm, 1453cm, 1645 cm, 1622 cm, 2944 cm, 2913 cm and 2845 cm were shifted and increased. In the brain, the intensity at 879 cm, 911 cm, 955 cm, 1223 cm, 1256 cm, 1304 cm, 1360 cm, 1453 cm, 1529 cm, 1636 cm, 2845 cm, 2915 cm and 2950 cm were increased and shifted. The most important changes of the fetus brain tissue are on the β structure of proteins due to the amide I bands at 1636 cm, while extensive effects on the DNA structure were obvious for the Phenobarbital treated liver tissues. As a conclusion, FTIR spectroscopy might well be assumed as a potentially powerful teratogenic measurement instrument with a unique ability to identify the modified bimolecular structures.