Turbulence modification by dispersed particles in a vertical, fully-developed channel flow was investigated by loading soft magnetic particles and locally applying a magnetic field to the flow, so that the significant transverse particle motion was observed. The attracted particles to a hot wall were detached from it after losing their magnetism at the excess temperature over particle Curie point. The application of magnetic force realized the capability to control the local particle concentration of particles in the channel and their velocities. The experimental results showed that the suppression of turbulence intensities in the core region was observed at a mass loading ratio of 0.18 and turbulence was much attenuated near the wall at 0.7. For accurate modelling the turbulence modification in particle-laden flows, it has been necessary to understand important parameters dominating the modification level. Parameterization performed in the present investigation showed that the ratio of particle diameter to a characteristic length scale of turbulence classified whether turbulence was damped or enhanced. Turbulence attenuation or augmentation levels in dilute two-phase flows were correlated with the particle Reynolds number based on mean relative velocities and the ratio of total particle velocity variance to total turbulence intensity, which will be dominant parameters in modelling a source or sink term of turbulence kinetic energy.