Abstract: A training device with alternative modules includes a main frame assembly, a front wheel assembly, a saddle, a pair of handbars and plurality of modular rear frame assemblies. The main frame assembly serves for mounting other components. This plurality of modular rear frame assemblies comprising a balance training rear frame assembly module and a pedal training rear frame assembly module. Either the balance training rear frame assembly module or the pedal training rear frame assembly module is removably attached to the main frame. In this way, could be quickly and conveniently converted from a balance bicycle to a conventional pedal bicycle. A user only needs to remove the fasteners holding the rear frame assembly to the main frame in order to finish such a conversion.