In seasonally dry tropical forests, fire is a significant determinant of forest dynamics. More frequent and intense fires predicted under climate change and slash-and-burn are likely to negatively affect forest sustainability, possibly through damages to fine roots and arbuscular mycorrhizal (AM) fungi. Here, we studied how a forest fire affects fine roots and AM fungi in Ankarafantsika National Park in northwestern Madagascar, which is nowadays threatened by anthropogenic fires. We conducted the present study in two stands; intact and fire-impacted stands within a seasonally dry tropical forest on quartz-rich white sand. Fine roots (diameter < 2 mm) were sampled in soil cores from 3 depths (0-5, 5-10, 10-20 cm depth) and separated into live or dead fine roots. Fine roots biomass and necromass were measured. AM fungal (AMF) colonization rate was quantified as the proportion of fine root segments colonized by AM fungi. Root diameter, length, surface area, and volume were measured from scanned images analyzed with SmartRoot software. Mean root diameter, specific root length (SRL), specific root area (SRA), and root tissue density (RTD) were calculated. Fine root production and decomposition were estimated from late dry season to the following early or late dry season using soil-ingrowth cores and root-decomposition cores. Fine root biomass at 0-5 cm depth was significantly lower in the fire-impacted stand than in the intact stand. Although there were no significant differences in fine root biomass at the other depths between the two stands, fine root biomass at the two depths was lower in the burned stand. The intact stand showed significantly higher AMF colonization rate at 0-5 cm depth than the fire-impacted stand in late dry season. However, AMF colonization rate at 0-5 cm depth in the fire-impacted stand increased in early dry season in the following year. Although there were no significant differences in root morphological traits between the two stands, roots in the burned stand exhibited more acquisitive traits (higher SRL and SRA, and lower RTD). The mean value of fine root production in the fire-impacted stand was half of that in the intact stand during wet season. Production and decomposition rates were relatively stable even in dry season in the former stand. These results suggest that root functional traits, AMF colonization, and fine root dynamics should be altered by fire and fire-impacts on aboveground vegetation, which could delay recovery of the seasonally dry tropical forest and influence nutrient cycling.