Background: Advances in American mink (Neogale vison) genomics have identified candidate genes linked to disease resistance, including RNF165, which is involved in immune response and virus–host interactions. Objectives: This study aimed to characterize genetic variation within the RNF165 (Ring Finger Protein 165) gene in farmed and wild mink to identify polymorphisms potentially associated with resistance to Aleutian mink disease virus (AMDV). Methods: Two groups of mink were analyzed: farmed animals from Latvia (n = 50) and wild animals (n = 20) from Poland. The presence of viral DNA was verified by PCR amplification targeting the VP2 and NS1 viral protein genes. To assess polymorphism within RNF165, primers spanning eight exons were designed, optimized, and applied in PCR amplification. PCR products were sequenced and subjected to bioinformatic analysis. Results: Two single nucleotide polymorphisms were identified: a synonymous substitution at c.G141A and a missense mutation c.G596A (p.R199K). Both variants were present in farmed and wild populations; however, the G allele at position c.141 was nearly twice as frequent in farmed mink compared to wild mink (p < 0.05). In silico functional prediction (SNAP2) indicated that the p.R199K mutation may moderately affect RNF165 protein function. Conclusions: Owing to its high conservation and role in immune regulation, RNF165 may serve as a promising candidate gene for molecular selection in breeding programs aimed at enhancing resistance to Aleutian mink disease (AMD).