Conventional deep fat frying is a common food preparation technique in Mauritius. The deterioration of soybean oil, commonly used in conventional frying, has been studied during frying of potato chips. The oil was subjected to continuous frying at 180 degrees C for a total of 600 min. The quality changes in soybean oil were evaluated at 90 min interval by Fourier transform infrared (FTIR) spectroscopy and some routine chemical parameters, namely peroxide value, iodine value and free fatty acid. An increase in hydroperoxide and free fatty acid concentration has been observed during the frying process by FTIR technique and the chemical parameters, peroxide value and free fatty acid respectively. A significant decrease in triglyceride ester linkage was observed by FTIR. The linear decrease noted for iodine value (P < 0.01) indicated a general loss of unsaturation. Furthermore, FTIR studies showed a loss of cis double bonds along with an increase in trans unsaturation. The formation of unsaturated aldehyde has also been observed during the frying process by FTIR technique.