We propose to determine the mass of isolated neutron stars through gravitational microlensing. We show that the all-sky microlensing pulsar event rate is ~2.8 × 10−10 per year per background source (/yr/source). Microlensing neutron star event rate would contribute ~20% to the total Galactic event rate at time-scale of ~15 days. We also present catalogue comparisons between known pulsars and background stars. We find that several pulsars would pass by background stars closely and may cause observable astrometric microlensing phenomenon. According to our covariance analysis, the uncertainty of masses determined through astrometric microlensing could be ~20%. Therefore, gravitational microlensing is a promising way to determine the mass of isolated neutron stars with future advanced radio and optical telescopes.