Fiber-shaped microsupercapacitors that have small volume and high flexibility are particularly needed due to the sudden high demand for appropriate power sources for wearable electronics, smart textiles, and microrobotics. For commercialization of fiber supercapacitors, an economical and mass-producible fabrication process is required. However, most wet-spun fiber supercapacitors are graphene-based electrodes that require complicated and dangerous post-treatment, such as using heat and chemical reaction. Here, continuous wet-spun fiber supercapacitors composed of manganese dioxide (MnO2), carbon nanotube (CNT), and platinum nanoparticle (PtNP) are fabricated by a simple one-step process. Low equivalent series resistance of 2.8 kΩ at 1 kHz and capacitance of 53.1 mF cm−2 are achieved from the MnO2/PtNP fiber supercapacitor. Because of good electrical conductivity, the rate capability remains at 60% from 10 to 100 mV s−1 in the three-electrode system. The wet-spun fiber supercapacitors and their manufacturing process are industrially useful because they have enhanced conductivity and electrochemical performance, can be mass-produced in a simple manner, and can be used in various fields, such as fiber-type batteries and solar cells, by altering the functional active materials.