The thermo-regulated sheath/core composite fibers containing 4-24 wt% of microencapsulated n-octadecane (MicroPCMs) were melt-spun with a 24-holes spinneret at a speed of 720 m/min. The polyethylene chips containing 10-60 wt% of MicroPCMs were used as the core and polypropylene chips were used as the sheath. The morphologies and properties of the chips and fibers were investigated by using SEM, DSC, WAXD and Melting Index tester etc. The microcapsules in the chips containing 10-40 wt% of MicroFCMs are evenly inserted inside the polymer matrix and their respective phase change temperatures are almost the same. The enthalpies rise steadily as the content of MicroPCMs increased from 10 wt% to 40 wt%. The efficiency of enthalpy of the chip containing more than 30 wt% MicroPCMs depends on the extruding procedure. For the same MicroPCMs content, the efficiency of enthalpy of the chip fabricated directly with MicroPCMs and polyethylene are significantly lower than that of the chips fabricated with polyethylene, MicroPCMs and chips containing MicroPCMs by progressively increase the MicroPCMs contents. Nonetheless, the spinnability of the chips decrease as the contents of MicroPCMs exceed 50 wt%. The micrographs of the spun fibers containing 4-24 wt% of MicroPCMs also indicate that the core of the fibers was evenly surrounded by the sheath component. The heat absorbing and evolving temperatures of the fibers remain unchanged with the increase of MicroPCMs content and keep at approximately 32 and 15 degrees C, respectively. The enthalpy, tensile strength and strain of the fiber containing 20 wt% of MicroPCMs are 11J/g, 1.8cN/dtex and 30.2%, respectively. The spun fibers can be used for the production of fabric materials. (c) 2005 Springer Science + Business Media, Inc.