One of the main challenges for tissue engineering is to create biomimetic microvasculature. The diameter of human capillary vessels ranges from 5 to 10 µm. To address this challenge, this project focuses on the fabrication of polycaprolactone (PCL) microtubes with a nanoporous structure by core-sheath humid electrospinning. The diameter of the microtubes ranges from 5.5-11 µm, and the nanopore size ranges from 200-1600 nm. This porous tubing structure closely resembles fenestrated capillaries. Through a series of experimental design, we discovered that the solvent type, ambient humidity, and solution viscosity have significant influences on fiber geometry and the core-sheath structure. Nanopores occurred when both the core and the sheath solutions adopted evaporative organic solvents. Consistent nanoporous microtubes were obtained by using the optimal viscosity and humidity levels for the core and the sheath solutions. Specifically, electrospinning of 10% PCL with 3% polyethylene oxide (PEO) as the core under 90% humidity resulted in helical microtubes. Suitable tube diameter and pore size were obtained for future endothelial cell adhesion and proliferation. Overall, this project showed a great potential to adopt the porous microtube network as the microvasculature for tissue engineering.