Post-fire regeneration was analyzed in a semideciduous mesophytic forest fragment in the county of Campinas (22º49'45'S and 47º06'33'W) Sao Paulo State, Brazil, in six surveys of the vegetation in natural regeneration, carried out at 20, 27, 35, 41, 48 and 66 months after a fire event. In each survey all the shrub and tree individuals with height >1.0 m were sampled in permanent plots. Pioneer species dominated the initial regeneration, with predominating density of Rincinus communis L. and Trema micrantha (L.) Blume that were gradually substituted by shade tolerant species. In the last surveys the understory and late secondary species substituted the pioneers, with predominating density for Hybanthus atropureus (A. St.-Hil.) Taub. and Galipea jasminiflora (A. St.-Hil.) Engl., that were probably favored by the shade produced by the speicies that started colonization in the area. The recovery of floristic richness in the forest fragment was relatively fast, since 27 months after the fire event 89 shrub and tree species were sampled and at 41 months this number had reached 116, that is close to the speicies richness found in mor preserved forest fragments in the region. Fire may be contributing to the great floristic heterogeneity in the semideciduous mesophytic forests, but in the long term the impact of this type of disturbance on the vegetation of fragments submitted to frequent fires is unknown. © 2005 Nova Science Publishers, Inc.