Objectives: Detennining the change of the serum IgE levels and correlation with the degree of decomposition of mast cells in patients with drug allergies. Subjects and Methods: This paper is a described and self-controlled study avaiable comparison in patients with drug allergies. Results: The rates of decomposition reaction of mast cells of the studied group, the control group, the patient group with the rapid allergic reaction and the patient group with the low allergic reaction are 86.66 percent, 6.66 percent (p 0.001), 91.30 percent and 59.10 percent (p 0.01) respectively.The general serum IgE level in average is 4644.52 +/- 2244.92 ng/ml. The serum IgE levels of the patient group with the rapid allergic reaction and the patient group with the low allergic reaction are 5322.80 +/- 2076.76 ng/ml and 4259.55 +/- 2385.51 ng/ml respectively. The serum IgE levels in average before and after treatment are 4644.52 +/- 2244.92 ng/ml and 3241.94 +/- 1878.13 ng/ml (p 0,05) respectively. The correlation between serum IgE levels and levels of decomposition of mast cells are positive linear correlation and hasclosely to equation Y