This study presents a new method for generating tunable and uniform magnetic alginate microbeads, which can be widely employed in the field of the bead-based bioassays such as sample pretreatment or immunoassays. The proposed microfluidic chip comprises pneumatically-driven vibrators to continuously spot alginate microdroplets in a thin oil layer. Continuously, the temporarily formed alginate microdroplets sank into a CaCl2 solution to become gelled microbeads. Besides, 8 microchannels with radiation-shape arrangement were designed to equally distribute the alginate/magnetic-nanoparticles suspension supplied by only one syringe pump. In addition the sandwiched fluorescent immunoassay (FIA) for the detection of dengue virus can also be carried out by utilizing the magnetic alginate microbeads. Therefore, the tunable and uniform magnetic alginate microbeads can be successfully generated and demonstrated for biological applications.