Abstract: Apelin is a hormone secreted from adipose tissue that has a role in many physiological processes and intrauterine growth, especially energy metabolism in the body, originating from a preproapelin of 77 amino acids. In this study, it was aimed to investigate the effect of Apelin on hormone response due to changes in Body Condition Score (BCS) in Simmental breed cows in different pregnancy periods. The study material consisted of 90 Simmental cattle aged 3-8 years with a clinically healthy appearance which were selected by random sampling at different pregnancy periods and BCS. Cows that made up the study material were divided into three groups according to their pregnancy period. The first group consisted of cattle in the first 3 months of pregnancy (n = 30), the second group consisted of cattle in 3-7 months of pregnancy (n = 30) and the third group consisted of cattle in the last 2 months of pregnancy (dry period) (n = 30). In blood serum samples taken from the jugular Vena of animals, the level of the hormone Apelin-36 was determined by ELISA technique. Serum Apelin-36 levels in the first 3 months of pregnancy, 3-7 months of pregnancy and last 2 months of pregnancy groups were determined as 0.66±0.009, 0.52±0.009 and 0.65±0.009 ng mL^–1, respectively. It was found that the effect of pregnancy status on serum Apelin-36 levels in cattle with BCS was found to be significant (p<0.01). As a result, it was concluded that the pregnancy status and BCS significantly affect the serum Apelin-36 level.