This study was built upon a large collection of bacteria, actinobacteria and fungi (1380 strains) previously isolated through an intensive sampling of a composting process and identified by molecular methods. This collection of strains supposed the entire cultivable microbiota associated to the composting process investigated. Since a significant number of strains were isolated many times, regardless of the temperature inside the composting piles (which ranged from 21.1 to 68.3 ºC), the starting hypothesis raised in this work was that a high thermotolerance can be found in the microbiota associated with the composting process. All strains were grown under laboratory conditions at 20, 30, 40, 50 and 60 ºC and growth at optimal temperature was recorded for each strain. In addition, the extent of growth inhibition at non-optimal temperatures was also measured. Results obtained showed a high thermal plasticity (thermotolerance) in the composting microbiome, since 90% of the strains grew at all tested temperatures. Only 9% and 1% of strains were classified as strictly mesophilic or strictly thermophilic, respectively. According to these results, the traditional conception of microbial groups succession throughout a composting process would need to be reassessed. Files in this dataset show the evolution of control parameters throughout the studied composting process and data from the experiments of quantification of growth at the assayed temperatures for the 1380 strains, as well as their taxonomic position.