This work has been led in view to find the influence of sublethal heat (45°C, 50°C, 60°C) on acid resistance of B. subtilis NCTC 3610 and B. stearothermophilus CNCH 5781 spores. Firstly, we have submitted Bacillus spores to 0.4% acetic acid pH 4.5 during the times of 1, 2 and 3 hours. Then another spores group were preheated at various sublethal temperatures, before be treated with acetic acid. The effect of acetic acid before and after preheat was evaluated by the culture of treated spores on agar medium and the number of colony obtained was compared with that of control culture (neither treated with heat nor acid) and control A culture (only treated with acid). We found that acetic acid was effective on the twice Bacillus spores with more effect on B. stearothermophilus CNCH 5781 spores. Furthermore we have noticed a significant increasing in percentages of recovery of colonies obtained from preheated and acid treated spores compared to those of control and control A cultures. This increase of recovery percentages could be demonstrated the manifestation of a "heat-induced acid resistance" phenomenon. Yet, this phenomenon was more accentuated for preheatings at 50 and 60°C during 3 and 2 hours, respectively for B. subtilis and B. stearothermophilus spores. This study suggest that sublethal heats could be play major role in protection of microorganisms to chemicals