Inertial focusing of particles in microchannels has demonstrated a great potential for a wide range of applications addressing various challenges, such as clinical diagnosis, biological assay, water treatment, etc. Even though numerous theoretical, numerical and experimental studies have been performed to identify the physical mechanisms underlying the migration of particles in confined environments, only a few works, up to now, have been devoted to the effects resulting from the interactions between particles of different sizes in polydisperse suspensions. In this work, high-speed bright-field imaging was used to experimentally analyse the behaviour of model bidisperse suspensions. The influences of bidispersity on (1) the lateral inertial migration of the particles towards equilibrium positions within the channel cross-section and (2) their longitudinal ordering into trains in the flow direction, were investigated under different conditions by varying the Reynolds number, the particles' size ratios and concentrations. The quantitative measurements and statistical analysis of the experimental data show that the bidispersity can modify not only the lateral migration process but also the sequential particle-ordering phenomenon.