Proteus mirabilis (P. mirabilis) is one of Gram-negative pathogens encountered in clinical specimens. A clinical isolate (TRP41) of P. mirabilis was isolated from a Turkish patient in Turkey. The isolate was identified using the API 32GN system and 16S rRNA gene sequencing and it was found resistant to ampicillin/sulbactam, piperacillin, tetracycline, and trimethoprim/sulfamethoxazole. This isolate was harboring a Class 1 integron gene cassette and its DNA sequence analysis revealed a novel bla(OXA) variant exhibiting one amino acid substitution (Asn266Ile) from bla(OXA-1). This new variant of OXA was located on Class 1 integron together with aadA1 gene encoding aminoglycoside-modifying enzymes. According to sequence records, the new variant was named as bla(OXA-320). Cassette array and size of integron were found as bla(OXA-320)-aadA1 and 2086bp, respectively. The bla(OXA-320) gene is not transferable according to conjugation experiment. In this study, we report the first identification of bla(OXA-320)-aadA1 gene cassette, a novel variant of Class D -lactamase, in P. mirabilis from Turkey.