Corpus luteum is a temporary endocrine gland, secretes progesterone and estradiol crucial for establishment and maintenance of pregnancy. The cyclin dependent kinase inhibitors (CDKIs) like p21 and p27 plays important role in cell cycle progression and regulation. In this experiment, the expression level of p21 and p27 mRNA and the proliferations of immune cells in different stages of the corpus luteum (CL) were studied. As p21 and p27 proteins are having role in the cell cycle progression and proliferation while CL undergoes both these processes. Ovaries containing corpora lutea were collected from local abattoir. The corpus luteum were isolated and segregated based on respective stages. The excised corpus luteum were processed for the extraction of the mRNA and a portion was embedded in paraffin for the slide preparation. The results showed significantly lower expression of p21 and p27 in stage I and -IV, compared to stage II and III (p <0.05). However, there was a slight dynamism in the expression level of each individual CL in the same stage, which indicates the developmental variation within the bovine specie. Histopathological examination shows that proliferation of immune cells gradually increased in stage I, II and III; however, a quick decline was found in stage-IV. The results indicate that p21 and p27 plays its role in the stage I (establishment) and stage IV (regression) of the corpus luteum. Decrease in immune cell proliferation in stage IV of the corpus luteum, as evident from histopathological examination, was probably the outcome of the increased apoptosis, triggered by down-regulation of p21 and p27. This indicates the reliance of apoptosis upon the expression level of p21 and p27. The level of p21 and p27 expression is indicative of estimating quality of the corpus luteum, and subsequently the early embryonic losses, associating mal functioning of the corpus luteum. Manuscript profile