The Nuclear receptor 1 family I member 3 (NR1I3), also known as the Constitutive Androstane Receptor (CAR), was initially characterized as a key regulator of xenobiotic metabolism. However, recent biochemical and structural data suggest that NR1I3 is activated in response to metabolic and nutritional stress in a ligand-independent manner. Thus, we prospected the Bovine NR1I3 gene for polymorphisms and studied their association with feed efficiency traits in Nellore cattle. First, 155 purebred Nellore bulls were individually measured for Residual Feed Intake (RFI) and the 25 best (High Feed Efficiency group, HFE) and the 25 worst animals (Low Feed Efficiency group, LFE) were selected for DNA extraction. The entire Bovine NR1I3 gene was amplified and polymorphisms were identified by sequencing. Then, one SNP different between HFE and LFE groups was genotyped in all the 155 animals and in another 288 animals totalizing 443 Nellore bulls genotyped for association of NR1I3 SNPs with feed efficiency traits. We found 24 SNPs in the NR1I3 gene and choose a statistically different SNP between HFE and LFE groups for further analysis. Genotyping of the 155 animals showed a significant association within SNP and RFI (p = 0.04), Residual Intake and BW Gain (p = 0.04) and Dry Matter Intake (p = 0.01). This SNP is located in the 5′flanking promoter region of NR1I3 gene and different alleles alter the binding site for predicted transcriptional factors as HNF4alpha, CREM and c-MYB, leading us to conclude that NR1I3 expression and regulation might be important to feed efficiency.