Canola and cottonseed oils were used in frying eggplant, potato and squash at 180 oC in the presence of air for a total period of 12 hours at 2 hours per day.  Changes in some physical and chemical characteristics as well as fatty acid composition were determined.  The results showed a gradual increase in peroxide value (P.V.) in all oil samples. Cottonseed oil showed a higher increase in P.V. than canola oil. Also, the T.B.A. value was increased gradually as frying time increased in all samples. The oil samples remaining after 12 hours of frying eggplant showed the highest increase in T.B.A. values than oil samples of potatoes and squash.

The obtained results showed that a gradual increase in the acid value (A.V.), saponification value (S.V.), C10:0, C12:0, C14:0, C16:0, C18:0, TSFA and ratio of C18:2: C18:1 with increasing frying time. In contrast, a gradual decline was observed in the iodine value (I.V.), C16:1, C18:1, C20:1, C22:1, TMUFA, C18:2n-6, C18:3n-3, TPUFA, TUFA as well as ratio of TUFA: TSFA. Furthermore, oxidation tests (P.V. and TBA.) used in this study revealed that TBA is consider as more reliable indicator to determine the degree of oxidation in heated oils and measuring the frying fat deterioration . Finally, it was suggested that canola oil had adequate deep frying characteristics like cottonseed oil.