This study reports the first records of the parasitism rates of the association among ectoparasitic flies of the family Streblidae found in phyllostomid bats in the state of Maranhão. Specimens were collected in patches of secondary forest and borders of mangrove in the village of Quebra Pote, located in the south portion of the island of São Luís. A total of 201 flies of 15 species and eight genera [Aspidoptera falcata Wenzel, A. phyllostomatis (Perty), Mastoptera minuta Costa Lima, Megistopoda aranea (Coquillett), M. proxima (Séguy), Speiseria ambigua Kessel, Stizostrebla longirotris Jobling, Strebla guajiro (García & Casal), S. hertigi Wenzel, Trichobioides perspicillatus (Pessôa & Galvão), Trichobius costalimai Guimarães, T. dugesii Townsend, T. dugesioides phyllostomus Guerrero, T. joblingi Wenzel and T. longipes (Rudow)] were collected from 50 individuals of nine species of phyllostomid bats [Artibeus lituratus (Olfers), A. obscurus Schinz, Carollia perspicillata L., Glossophaga soricina Pallas, Lophostoma carrikeri J A Allen, Micronycteris minuta Gervais, Phyllostomus discolor Wagner, P. hastatus Pallas and Sturnira lilium E Geoffroy)]. Mastoptera minuta, T. costalimai, T. longipes, A. falcata and S. longirostris, were the most frequently found ectoparasites, present in at least 50% of the infected bats. Two species of bats, C. perspicillata e P. discolor, showed the highest richness of ectoparasites, with four species of flies each, and an infection rate of 46% and 100%, respectively.