Oxidised low density lipoprotein receptor 1 ( OLR 1) is a type II membrane protein that belongs to C-type lectin family that acts as a cell surface receptor for oxLDL. This receptor is coded by OLR 1 gene. With regard to the role of OLR 1in lipid metabolism in degrading oxLDL and QTL studies for milk production traits, OLR 1 has been regarded as a candidate gene related to milk production traits in dairy cattle. One polymorphism () in 3' untranslated region of this gene might control translation or stability of OLR1 mRNA. This polymorphism is the result of substitution of nucleotide adenine by cytosine in position 8232 ( OLR 1g.8232 C A). In the case of being nucleotide C, there will be restriction site for the restriction enzyme Pst I and as a result, alleles A and C will be recognizable as bands with length 270bp and 250bp respectively. To hnvestigate this polymorphism and its relationship with milk production traits, blood sample was randomly taken from 408 Holstein cattle in 5 industrial dairy farms located in Isfahan province that had records for milk production and its composition for first parity. Genotyping was done by PCR-RFLP technique. After extracting DNA, determining the quality and quantity of extracted DNA, amplification and digestion by restriction enzyme, digestion product was observed on 2.5% agarose gel. Both alleles A and C were observed in all 5 herds and wich their frequencies werw 0/5172 and 0/4828 respectively totally. Frequency of genotypes AA, AC and CC werw also 0/289, 0/456 and 0/255 respectively. All five herds and all of them were in Hardy–Weinberg equilibrium. Being in equilibrium can be owing to selecting animals according not to OLR 1 gene. Genetic analysis of the population was done by the software PopGen32. Resulted indices indicates high diversity of this polymorphism and high inbreeding and genetic relationship in the studied population. To identify the effect of genotype on production traits, the software SAS, procedure GLM was used. In the analysis model the effects genotype and combined effect of herd, year and season of parturition were considered as fixed effects and days in lactation and open days were considered as covariables. Genotype had significant effect on fat and protein percentage and the breeding value of milk fat production (P 0/001). Individuals with genotype CC had statistically more milk fat percentage and breeding value of milk fat production in comparison with genotypes AC and AA. Also cows having genotype AC showed more milk fat percentage compared to genotype AA. This finding can be a reason that the effect of this polymorphism is additive. Also individuals with genotype CC and AC had more milk protein percentage in comparison with genotype AA. For traits milk fat percentage, milk protein percentage and the breeding value of milk fat production, the average effect of substitution of allele C was significant (P 0/001), but dominance effect for the studied traits was not significant (P 0/05) which indicates the effect of the polymorphism as additive. Regarding the relationship between the polymorphism and traits milk fat percentage, milk protein percentage and the breeding value of milk fat production and also its hight diversity in the studied population, the polymorphism can be used is selection for these traits.