Non processed onion (Allium cepa L.) powder or onion powder processed with ${eta}-cyclodextrin+1%$ calcium chloride+1% soluble starch solution was added to the diet of 16 week old Wistar and spontaneously hypertensive rats (SHR) for 5 weeks. 36 SHR and Wistar rats were randomly divided into 3 diet groups, each of six. They were named control, NPO (non processed onion), PO (processed onion). The rats of the control group were fed diet without onion powder. To NPO and PO groups were added 5% of non processed onion and processed onion, respectively. Body weight gain, food efficiency ratio (FER), blood pressure, angiotensin converting enzyme (ACE) activity and Na excretion of urine and feces were analyzed. The processed onion and non processed onion diet reduced body weight gain without affeting the total food intake in Wistar rats (p<0.05). The body weight gain was lowest in Wistar rats fed with a diet with processed onion powder. The rats fed with diet containing PO or NPO had lower blood systolic blood pressure in SHR (p<0.05). The effect of onion powder on decreasing the blood pressure was not significant in Wistar rats. The ACE activity in lung was lowered in the SHR fed with either PO or NPO (p<0.05) compared to those fed with control diet. The urinary Na excretion was significantly lower in SHR than Wistar rats. The effects of PO and NPO on increasing the urinary and fecal excretion of Na were significant (p<0.05). These results suggest that onion processed with ${eta}-cyclodextrin+1%$+1% calcium chloride+1% soluble starch solution to reduce volatile flavor, browning and caking preserves an antihypertensive effect of non processed onion.