The objective were to determine which aerobic bacteria produce marked effect on cystic endometrial hyperplasia-pyometra complex (CEH-P) and where they sourced from, and analyze the relations of progesterone and estrode concentration in bitch blood with CEH-P.Forty-eight privately owned bitches were diagnosed as CEH-P including pyometra and endometritis by history, physical examination, ultrasonography, ovariohysterectomy and histopathological examination.Healthy vagina and uteri samples were obtained with cotton pledget, and uteri cumulative fluids of CEH-P cyst were collected with syringe in vitro for aerobically bacterial isolation and identification; sera were brought back to laboratory to detect progesterone and estrode levels respectively with Iodine [~I] Progesrerone Radioimmunoassay Kit and Iodine [125I] Estradiol Radioimmunoassay Kit.Total of 99 isolates were identified, and the main aerobes in CEH-P were Escherichia coli (33/99), and the next in order were Salmonella enterica (14/99), Proteus mirabilis (13/99), Pseudomonas aeruginosa (13/99), Staphylococcus aureus (12/99), Streptococcus agalactiae (7/99), Shigella(6/99) and Corynebacteria(1/99).Thereinto, Escherichia coli, Salmonella enterica, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus and Shigella could be isolated from healthy vagina.The levels of estrode in endometritis, pyometra and estrus bitches were higher than that of in diestrus bitches(p<0.01).In addition, the level of estrode was higher in CEH-P bitches than in estrus bitches(p<0.05).Estrode level in endometritis bitches was different from that of in estrus bitches(p<0.01).No difference of estrodiol level was found between endometritis and pyometra bitches(p >0.05).Progesterone levels were different among all four groups (p<0.01), in the order from high to low were pyometra, endometritis, estrus and diestrus bitches.Animal experiment validated that bacterial inoculation in uteri was failed without hormone stimulation advance.It suggests that, in addition to common pathonenic bacteria differential in every area, casual bacterial contamination invariably occurred in bitch CEH-P, and the main infection was ascended from vagina while the cervix opened.We also inferred that both estrode and progesterone levels in CEH-P bitches were increased than in healthy bitches,and even higher than that of in estrus bitches.Estrode and progesterone pretreatment and uterine mucosa damage were interpreted as the precondition of bacterial infection.These characters of hormone levels in CEH-P bitches should be similar with the endocrinal characters in peripartum bitches.