This protocol describes the design of capillary microfluidics for spinning bioactive (cell-laden) microfibers for three-dimensional (3D) cell culture and tissue-engineering applications. We describe the assembly of three types of microfluidic systems: (i) simple injection capillary microfluidics for the spinning of uniform microfibers; (ii) hierarchical injection capillary microfluidics for the spinning of core-shell or spindle-knot structured microfibers; and (iii) multi-barrel injection capillary microfluidics for the spinning of microfibers with multiple components. The diverse morphologies of these bioactive microfibers can be further assembled into higher-order structures that are similar to the hierarchical structures in tissues. Thus, by using different types of capillary microfluidic devices, diverse styles of microfibers with different bioactive encapsulation can be generated. These bioactive microfibers have potential applications in 3D cell culture, the mimicking of vascular structures, the creation of synthetic tissues, and so on. The whole protocol for device fabrication and microfiber spinning takes ~1 d.