Objective To explore the effect of Modified Lianggu Decoction（两固汤加减） on endometrial receptivity during the implantation window of ovulation induction model mice

and the underlying mechanism. Methods Totally 144 female ICR mice were randomly divided into natural cycle group

ovulation induction group

progesterone group

and Modified Lianggu Decoction group

with 36 mice in each group. Normal saline 0.2 ml/10 g（body weight）

progesterone 0.4 mg/10 g

and Modified Lianggu Decoction 0.3 mg/10 g were administered by gavage

once daily

for 15 days in ovulation induction group

progesterone group and Modified Lianggu Decoction group

respectively. After nine days of gavage

pregnant mare serum and triptorelin acetate injections were used to establish a model of ovulation induction in female mice of ovulation induction group

progesterone group and Modified Lianggu Decoction group

while equal volume of normal saline was injected in natural cycle group. After last injection

female and male mice at a ratio of 2 ∶1 were caged in each group. The vaginal plug

number of embryo implantation

histological changes of the endometrium during implantation window

and the number of spiral arteries in the endometrium were assessed on the next morning. Mice were sacrificed after mating day

with six mice per day since the 2 nd day. The expression of macrophage inflammatory protein 1β（MIP1β）

CD244

and uterine natural killer cell（uNK） protein were detected. Results The number of embryo implantation in ovulation induction group significantly decreased on the 2 nd day after the mating day

while the number of spiral arteries in the endometrium decreased on the 4 th day compared to natural cycle group（P<0.05）. Compared to ovulation induction group

there were significantly larger numbers of embryo implantation and spinal arteries in the endometrium in progesterone group and Modified Lianggu Decoction group（P<0.05）. The expression of CD244 and uNK protein significantly decreased on the 4 th and 5 th day in ovulation induction group compared to the natural cycle group

and were elevated in progesterone group and Modified Lianggu Decoction group compared to the ovulation induction group（P<0.05）. Modified Lianggu Decoction group had the highest expression of CD244 and uNK protein on the 4 th day compared to progesterone group and natural cycle group（P<0.05）. Conclusion Modified Lianggu Decoction may improve the endometrial receptivity during implantation window and promote embryo implantation of ovulation induction model rats

by regulating the disorder of uNK and CD244 protein expression.