Objective To study the possible mechanism of Modified Guominjian Decoction（ 加味过敏煎） in treating urticaria. Methods A total of 60 BALB/c mice were randomly divided into blank group

simple IgE group

model group

Guominjian Decoction group

Modified Guominjian Decoction group and loratadine group

with 10 rats in each group. The Guominjian Decoction group was given Guominjian Decoction 10. 27 g/（ kg·d）

and the Modified Guominjian Decoction group was given Modified Guominjian Decoction 14. 39 g/（ kg · d）

the loratadine group was given loratadine pills 2. 10 mg/（ kg·d）

and the model group

blank group and simple IgE group were given equal volume normal saline

once a day

for constant 7 days. On the 6 th day

except for the blank group

the other groups were injected with 0. 5 ml of anti-DNP IgE monoclonal antibody in the tail vein. The next day

except for the blank group and the simple IgE group

the ears of the other groups were smeared with 2 4-dinitrofluorobenzene 50 μl to activate for the establishment of the animal model of urticaria. On the 8 th day

the degranulation of skin mast cells

the expression of protease activated receptor 2（ PAR-2） mRNA and serum histamine concentration were detected in each group. Results With the observation of microscope

there was no obvious degranulation of mast cells in the blank group and the simple IgE group. The degranulation of mast cells in the model group was obvious. The number of degranulation of mast cells in each administration group was lower than that in the model group. The number of degranulation in the Guominjian Decoction group was relatively small. Compared with the blank group and the simple Ig E group

the number of degranulation

PAR-2 mRNA and histamine expression in the model group were significantly increased（ P < 0. 05 or P < 0. 01）. Compared with the model group

the number of degranulation

PAR-2 mRNA and histamine expression in the Modified Guominjian Decoction group were significantly decreased（ P < 0. 01）

and were decreased more than those in the Guominjian Decoction group and the loratadine group（ P < 0. 05 or P < 0. 01）.Conclusion The Modified Guominjian Decoction may down-regulate the expression of PAR-2 in the skin

reduce the release of serum histamine

inhibit the degranulation of skin mast cells

stabilize mast cells to achieve the function of treating and preventing urticaria.