OBJECTIVE： To compare antidiuretic activity of Ootheca Mantidis before and after processing， and to explore the best medicinal part and mechanism of Ootheca Mantidis. METHODS： 96 rats were randomly divided into blank group， model group， positive group， Ootheca Mantidis group， Ootheca Mantidis stir-fried with salt group， steamed Ootheca Mantidis group， crude product eggs and egg shell groups， processed product eggs and egg shell groups， with 8 rats in each group， 12 groups in total. Except blank group， other groups were given adenine 250 mg/kg， ig， for 4 weeks to induce kidney-yang and diuresis model. From third week， Ootheca Mantidis crude drug group and processed Ootheca Mantidis group were all given relevant medicine 0.11 g（crude drug）/ml i.g， and crude product eggs and egg shell groups and processed product eggs and egg shell groups were given relevant medicine， ig， once a day， by mass ratio of eggs to egg shell （cude drug 1 ∶ 2.4， salt stir-fried product 1 ∶ 1.7， steamed product 1 ∶ 2.1） for consecutive 4 weeks. The urinary volume， body weight， renal index and the serum contents of ADH and ALD were all determined. RESULTS： Compared with blank group， body weight and serum content of ADH and ALD decreased in model group， while renal index and urinary volume increased （P＜0.05）. After 4 weeks of treatment， compared with model group， body weight and serum content of ADH increased in Ootheca Mantidis groups， while urinary volume and renal index decreased （P＜0.05）； serum content of ALD increased in treatment groups； there was statistical significance in the serum content of ALD in those groups except Ootheca Mantidis group， Ootheca Mantidis stir-fried with salt group and steamed Ootheca Mantidis group （P＜0.05）； except for ALD， those index were in descending order of steamed Ootheca Mantidis group＞Ootheca Mantidis stir-fried with salt group＞Ootheca Mantidis group， and steamed Ootheca Mantidis shell group had best exchange. CONCLUSIONS： The antidiuretic activity of Ootheca Mantidis has been enhanced after processing. The egg shell of steamed Ootheca Mantidis is main medicinal part. To increase the serum content of ADH might be one of the main mechanism of arresting polyuria.