Turbulence modulation in rotating channel flows due to small solid particles, at low particle volume fractions O(10(-5)), is studied using direct numerical simulation (DNS). It is found, for the larger and heavier particles in a rotating channel, that the consideration of inter-particle collisions in the modeling yields higher turbulence kinetic energy as compared to the one without consideration of the inter-particle collisions. From the present DNS results, it is shown that, the inter-particle collisions enhance the fluid turbulence energy in the central region mainly at low wavenumbers; the inter-particle collisions enhance the fluid turbulence energy in the near-wall regions in the whole spectral band. The 70 mum copper particles have a positive contribution in the vicinity of the pressure surface and a negative contribution a little far from it to (u(2)) over bar and (v(2)) over bar, while a negative contribution to (uv) over bar in the vicinity of the pressure surface. The dissipation and viscous diffusion are changed consequently in this area. When the inter-particle collisions have not been considered, the magnitudes of the peaks of terms in balance of the Reynolds stress equations are much damped near the pressure surface and their positions are moved away from the wall, and there is almost no gain or loss near the suction surface compared with the corresponding case considering the inter-particle collisions. Production term G(12) due to system rotation plays an important role in the (uv) over bar equation, especially for the cases not considering the inter-particle collisions. (C) 2002 Elsevier Science Ltd. All rights reserved.