Resumo. The root maggot fly, Delia sanctijacobi (Bigot, 1885) (Diptera: Anthomyiidae) is an important pest of several commercial crops. In this note we report for the first time the occurrence of D. sanctijacobi damaging soybean (Glycine max (L.)) crops in Brazil. The specimens were collected from commercial soybean fields in Saldanha Marinho and Cruz Alta, both in Rio Grande do Sul state, Brazil. The attacked soybean plants showed damaged roots, bored stem and reduced plant stand. The species was confirmed by morphological traits and DNA sequencing. The first detection of D. sanctijacobi on soybean in Brazil raises an alert to growers and highlights the need for development of efficient and sustainable management strategies for this emergent pest.