This paper presents numerical results on the near-field interactions of particle-laden twin supersonic jets operating in underexpanded mode, with special emphasis on the effects of particles on jet flow expansion. Although plane jets have been considered primarily, a few cases of twin round jets have also been simulated for the sake of comparison. Three turbulence models (Spalart-Allmaras, k-ε (realizable), and k-ω (sst)) have been considered for incorporating turbulent interaction effects in two-phase supersonic jets. In general, the k-ω (sst) model gives better predictions in the reverse flow as well as in the shock regions. The recirculatory flow is enhanced at high underexpansion (UE) ratios, and the size and strength of the recirculation region are much smaller for twin round jets than those for plane jets. In particle-laden jets, small particles (corresponding to Stokes number less than 0.05) are entrained in the recirculation zone, whereas particles of larger size are not trapped. With large particles, a particle-free zone occurs close to the nozzle wall in the divergent section. Small particles follow the gas phase with negligible non-equilibrium effects, but they also cause higher two-phase drag, resulting in a higher degree of jet UE.