This study was aimed to evaluate the relationships between body condition score (BCS) and milk production traits using Bayesian approach. The records were obtained during years 2006 to 2014 from the cooperative dairy cattle union (VAHDAT) across 16 dairy herds in Isfahan province. Estimats of the correlation between BCS and test day records of milk was used to identify which test day correlation show higher relationship during milk period. Number of the records for body condition score(BCS), milk production, fat percentage of milk, protein percentage of milk and somatic cell score(SCS) were 164264, 164281, 151249, 153344 and 155160 records respectively. After editing data the files of records and pedigree were prepared. For estimating the genetic parameters, a multiple-trait random regression animal model was used accurding to Gi sampling method in BLUPF90. Average of the heritability BCS, milk yield, fat percentage, protein percentage and somatic cell score were 0.26, 0.34, 0.20, 0.18 and 0.20 respectively. This study show that on an average daily basis, BCS was genetically unfavorably(negative) correlated with milk yield, but genetic correlations between BCS and other traits were positive. The negative genetic correlation between BCS and milk yield showed that using one of this traits without considering the other could change the genetic potential in the population. Therefor both of thiese traits could be improved by simultaneous choosing in a dairy breeding plan. However less progress observed in milk yield but by using Gi method the health and reproduction traits would be positively change. Keywords: Random regression, Bayesian approach, Milk production, Body condition score
