RESUMO: Parasitoids of the genus Aleochara play an important role in the natural regulation of cyclorrhaphous Diptera of medical and veterinary relevance, many of which are associated with decomposing substrates and are of forensic importance. Aleochara (Aleochara) lustrica Say, 1832 (Coleoptera: Staphylinidae) is distributed across the Americas but, despite records from several Brazilian states, had not previously been reported from Rio Grande do Sul, and its host associations remain poorly documented. In this study, we report the first occurrence of A. (A.) lustrica in Rio Grande do Sul, Brazil, extending its known southern distribution limit in the Americas. Field sampling was conducted between April and May 2025 at the Pelotas – Visconde da Graça Campus (IFSul), using poultry liver as bait to attract ovipositing flies. Pupae recovered from the substrate were reared individually under controlled laboratory conditions. Among 178 field-collected sarcophagid pupae, 61 (34.26%) were parasitized, yielding nine adult specimens of A. (A.) lustrica. Although parasitized puparia were morphologically highly consistent with Microcerella halli (Engel, 1931) (Diptera: Sarcophagidae), species-level host identification for field-parasitized pupae could not be formally confirmed and is therefore conservatively interpreted at the family level (Sarcophagidae). Laboratory assays confirmed M. halli as a suitable host for A. (A.) lustrica, representing the first confirmed association between this parasitoid and a sarcophagid fly under controlled conditions. These findings expand current knowledge of the geographic distribution and host range of A. (A.) lustrica and document a previously unreported interaction of relevance to ecological, veterinary, and forensic entomology.