The present study was conducted to investigate the toxicity of potassium nitrate on blood serum glucose, cholesterol levels, alanine aminotransferase (ALT), Aspartate aminotransferase (AST) activity levels, and the possible ameliorative effect of ascorbic acid (Vitamin C). Male Wister rats are used as experimental model divided into three groups (each of 6-8 rats) and treated for six weeks as follows: Group 1 : served as control: Group 2 : received 2 % potassium nitrate added to the concentrated forage and Group 3 : received 2 % potassium nitrate together with 1 % ascorbic acid added to rat's concentrat forage. Nitrate treatment in group 2 leads to high significant increase in serum levels of glucose on 3^rd, 4^th, and 5^th weeks, cholesterol level increased significantly on both 4^th and 5^th weeks, while ALT activity levels increased on the 4^th, 5^th and 6^th weeks, and AST increased significantly on the 5^th and 6^th weeks. Addition of ascorbic acid with potassium nitrate, lead to reverse all the parameters nearly to normal. It was concluded that potassium nitrate causes significant toxic effect on some blood serum biochemical parameters which were ameliorated by ascorbic acid.