The Brazilian Atlantic forest is a biodiversity hotspot and harbors many endemic species showing peculiar and unique traits. However, it has been reduced to less than 8% of its original surface and is distributed in scattered fragments, the great majority of which are smaller than 20 hectares and very disturbed, making it worth asking about their value for conservation. In this paper we assess the refugium value of small fragments to the conservation of one of the endemics of the Atlantic forest, the ovoviviparous cockroach Monastria biguttata. Our results showed that this species was ubiquitous in large and small forest fragments, but never present in plantations or pastures. The population age structure and sex ratio were balanced in every fragment, and total population size in the smallest fragments was at least several hundreds of individuals. Colony size, sex ratio, age structure, and density per piece of dead tree trunk indicated that populations from small fragments were not unbalanced or at risk of extinction. According to the analysis of resource availability, small fragments can provide suitable habitat for this species. In this situation, even very small forest fragments have a high refugium value for some endemic insect species. Considering their number in the landscape, these fragments should be considered with more attention in strategies of biodiversity conservation.