The polyimides formed from the polymerization of monomeric-reactants (PMR) approach have been increasingly used as matrix materials in fiber-reinforced composites on aerospace and space structures for high temperature applications. The performance of PMR-based structures depends on the mechanical durability of PMR resins at elevated temperatures, including creep and stress relaxation. In this work, the creep behavior of PMR-15 resin was studied using the impression technique in the temperature range of 563-613 K and the punching stress range of 76-381 MPa. It was found that there existed a steady state creep for the creep tests performed at temperatures of 563 K and higher, from which a constant impression velocity was calculated. The steady state impression velocity increased with temperature and punching stress with the stress exponent in the range of 1.5-2.2. The average of the apparent activation energy of the PMR-15 was calculated as 122.7 +/- 6.1 kJ/mol. POLYM. ENG. SCI., 50:209-213, 2010. (C) 2009 Society of Plastics Engineers