The aim of this study was to assess the influence of genotypes from the CSN3 and LGB loci on milk production and chemical composition in Romanian Simmental cattle (n=114). For the CSN3 locus a significantly higher frequency (P≤0.001) was observed for the allele A (0.785) compared to allele B (0.215) and for AA (0.631) compared to AB (0.307) and BB (0.062) genotypes, respectively. The AA genotype was associated with a higher milk production (5887.76±115.7 kg) compared to the yields associated with the BB genotype (5619±86.34 kg, P≤0.003), as well as a higher fat percentage (4.19±0.05% vs. 4.01±0.02%, P≤0.001). A higher milk protein percentage was associated with BB (3.4±0.02%) compared to AA (3.27±0.03) and AB (3.29±0.03) genotypes, respectively (P≤0.05). For the LGB locus, the frequency of allele A was significantly higher (0.606, P≤0.008) than allele B (0.394). The AB genotype was the most prevalent in the herd (0.579) compared to AA (0.316) and BB genotypes (0.105). The AB genotype was associated with a higher milk production (5906.54±166.76 kg) compared with the other two genotypes (P≤0.05). The BB genotype was associated with a higher fat percentage in milk (4.23±0.06%) compared with AA (4.17±0.06) and AB (4.2±0.08) genotypes, respectively (P≤0.01). For the LGB locus, no significant differences (P>0.05) were observed for milk protein percentage. In order to increase the quantity and quality of milk, the outcomes obtained in this study encourage improving genetic structure in cattle based on marker assisted selection for genes with economic values.