Extremely flexible hollow optical fibers with 75-μm-bore size were developed for infrared laser light delivery. The hollow fiber was inner coated with silver and dielectric layers to enhance the reflection rate at an objective wavelength band. The silver layer was inner-coated by using the conventional silver mirror-plating technique. Concerning the fabrication parameters used up to now for 320-μm-bore size fibers, the target flowing rate for plating solutions was 10 ml/min. Parallel arranged bundles of silica capillaries were used to increase the cross-sectional area of the air core. To achieve the flow-rate target, four bundles of 300 pieces of silica capillaries with an inner/outer diameter of 75/150-μm and a length of 20 cm were bundled. To increase the flow rate, four bundles with an inner diameter of 75-μm and a length of 20 cm, together with three silica capillaries with an inner diameter of 530-μm and a length of 50 cm were connected in parallel. The spectrum loss measured by an optical spectrum analyzer for the 75-μm-bore size, 10-cm-length silver hollow optical fiber was around 5 dB at the wavelength of 1-μm. Thin dielectric layer was formed by using liquid-phase coating method for low-loss transmission of Er:YAG laser light.