This study was conducted to investigate the relationships between body weight (BW) and milk yield, and post-partum BW and their changes during parity and stage of lactation in Holstein cows. This study was conducted on a private dairy cattle farm in Kastamonu province in the Mid-Black Sea Region of Turkey. The study material included 2133 records from 273 Holstein cows calved between 2016 and 2017 years. Parity (from 1 to 5) and stage of lactations (from 1 to 10) were used to be environmental factors affecting traits. The effect of parity and stage of lactation on BW and milk yield were significant (P<0.05). BW and milk yield increased with advancing lactation until the fourth parity, then declined in the fifth parity. The lowest BW was observed in the first two months of lactation, and it increased linearly with following lactation periods. Milk yield was low in the first month of lactation and then decreased linearly until the end of lactation. Correlations between BW and milk yield were all positive and ranged from 0.201 to 0.588. BW changes in early to mid-lactation were phenotypically correlated with milk yield. Finally, based on the findings in present study, it is suggested that monitoring BW change in early and mid-lactation can be used as a management tool to improve the milk yield in dairy herds.