Trichoderma reesei is a biotechnically important filamentous fungus used commercially in enzyme production. T. reesei is used to produce low cost enzymes for the conversion of plant biomass materials into industrially useful bioproducts such as sugars and bioethanol. We explored transcriptional responses of T. reesei to heat shock stress. DNA microarrays were used to characterize changes in the gene expression profiles of approximately 2000 T. reesei transcripts in response to heat shock caused by temperature increase to 40^oC. The fungi was grown for 16 h at 28^oC with shaking at 200 rpm. After this, mycelia were collected, washed, and transferred into fresh medium. The incubation was continued for two hours at 28^oC before the control mycelial was harvested. After three hours, the culture was quickly transferred from 28^oC to 40^oC water bath. To monitor the time course of transcriptional responses, mycelia were harvested 15min, 30min and 60min after the transferred at 40^oC. Finally, the mycelia were returned at 28^oC and were harvested after one hour. The results showed that 104 genes were induced and 106 genes were repressed by heat shock. Gene that encode Hsp70, Hsp90 proteins associated with cellular defense, like chaperones, had their expression induced. They are probably involved in protein folding or degradation. The transcriptional responses of proteins associated with cellular division like H4, Nhp6a, EsdC and protein synthesis like ribossomal proteins were repressed. This work can provide a better understanding of cellular processes and may support future projects for a better adaptation of this organism to industrial conditions.