The precipitation kinetics of secondary phases in a 10.5%Cr heat resistant steel, designed by the authors, was studied experimentally and theoretically. Experimental data of nucleation, growth and coarsening stages for M23C6 carbides, V-MX, Nb-MX and Laves phase were obtained by HRTEM-characterization on samples after tempering (780 degrees C/2 h) and isothermally aging for 1440 h and 8760 h at 650 degrees C. Theoretical studies of precipitation behavior of M23C6 and Laves phase were carried out by TC-PRISMA and complemented with DICTRA. A good fit between TC-PRISMA simulation and experimental results was obtained for M23C6 carbides considering a heterogeneous nucleation in grain boundaries, a semi-coherent interfacial energy of 0.3 J/m(2), and decreasing the atomic mobility along grain boundary in order to include the effect of B. Experiments and simulation indicate a low coarsening rate for M23C6 carbides. Furthermore, precipitation of Laves phase at 650 degrees C was simulated by TC-PRISMA considering the effect of W and Si segregation at grain boundary, prior to the beginning of the nucleation and growth processes. Therefore, thermodynamic and kinetic boundary conditions were changed purposely in TC-PRISMA. Best agreement with the experimental results was obtained for an interfacial energy of 0.6 J/m(2) and heterogeneous nucleation in grain boundary. (C) 2017 Elsevier B.V. All rights reserved.