Abstract: Background and Objective: Extra virgin olive oil is consumed in most areas of the Mediterranean and the tropics and has been reported to be involved in the lowering of arterial blood pressure. The aim of this study was to determine the possible mechanism of arterial blood lowering effect of extra virgin olive oil and palm oil diets. Materials and Methods: Male Wistar rats (10 rats per group) were fed on normal rat chow (control), Fresh Palm Oil (FPO), Extra Virgin Olive Oil EVOO) and Thermoxidized Palm Oil (TPO) groups. The oil-fed groups received 15% (weight/weight) of oil mixed with rat chow for 18 weeks. Blood pressure was measured by direct cannulation and blood samples, heart and kidney were collected for biochemical analysis. Results: The basal Systolic Blood Pressure (SBP) and after phenylephrine (10–6 mmol L–1) infusion was significantly (p<0.01) elevated in EVOO, FPO and TPO compared with control. Levcromakalim (10–6 mmol L–1) (a KATP-channel opener) and NS1619 (Bkca channel opener) infusion significantly (p<0.01) reduced mean arterial pressure (MAP) in FPO and EVOO compared with control and TPO. Heart and kidney SOD and catalase activities were significantly (p<0.05) increased in EVOO and FPO groups when compared with other groups but decreased in TPO. Conclusion: Long term intake of thermally oxidized palm oil may suppress potassium ion channel function thereby increasing blood pressure. Blood pressure reduction property in FPO and EVOO is via KATP and Bkca ion channels and the greater effect of EVOO is probably due to its high content of oleic acid and polyphenols.