Thermo-kinetic simulation of precipitate evolution during long-term thermal exposure in ferriticmartensitic heat-resistant power plant steels (P91 and P92) is carried out using MatCalc software, in combination with a Gibbs energy database and a mobility database for steels that come with MatCalc. MX and M 23C 6 are predicted to remain as major precipitates during long-term thermal exposure in these steels. Average size of MX precipitate is found to vary between 10 and 50 nm in both steels, while M 23C 6 exceeds 100 nm in the case of P91 after 1000,000 h of thermal exposure at 600 °C. The simulated precipitation sequence and precipitate size evolution during thermal exposure are in good agreement with available experimental data. It is expected that the calculations presented here give insight into long-term microstructural stability of ferriticmartensitic steels under service conditions, which is otherwise difficult to establish by experiments alone. © 2011 Elsevier Ltd. All rights reserved.