Abstract In this study, a low-loss hollow-core photonic bandgap fiber (HC-PBF) with an isolated anti-resonance layer is proposed. The fiber cladding structure is the same as that of conventional HC-PBF, while the fiber core is surrounded and formed by an isolated anti-resonance layer which separates the core from the cladding. Simulation results show that the overlap between the fundamental mode and silica-air interfaces is dramatically reduced owing to introduction of the isolated anti-resonance layer, and the fiber loss lower than 3.5 dB/km can be achieved with only ∼ 13- μ m core diameter and ∼ 8- μ m mode field diameter at 1550 nm