There seems to be no method available to measure all parameters of interests in multiphase flow systems with high solids concentration and with reasonable accuracy. Parameters include, local particle velocity vectors, solids volume fractions and bubble rise velocity, size, frequency and volume fraction. In this study a novel method based on a fiber optical technique and tracer particles has been developed for simultaneous measurements of the mentioned local flow properties in highly concentrated multiphase flow systems such as gas-solid fluidized bed reactors. A particle present in the measuring volume in front of the probe is marked with a fluorescent dye. A light source illuminates the particles and the detecting fibres receive reflected light from uncoated particles and fluorescent light from the tracer particle. Using optical filters, the fluorescent light can be distinguished and together with a small fraction of background light from uncoated particles can be used for the determination of local flow properties. The method gives the possibility for simultaneous measurement of the local movement of a single tracer particle, local bubble properties and the local solids volume fractions in different positions in the bed.