Direct numerical simulations of spatially developing turbulent boundary layer laden with small, heavy particles are performed at low Reynolds number. The effects of particle gravity settling on the turbulent/non-turbulent interface are discussed by comparing the new simulations with previous simulations laden with inertial particles. The results reveal that heavy particles reduced the height of the interface but increase the complexity of the interface by stretching the boundary downwards and generating extra small-scale structures. Different degrees and positions of particle accumulation beneath the interface, together the gravity settling of heavy particles, result in nonmonotonical changes of the thickness of the interface layer which is apparently different from inertia-particle cases.