We report on the detailed transport, magnetic, thermodynamic properties and theoretical calculation of KBi2 single crystals in superconducting and normal states. KBi2 exhibits metallic behavior at a normal state and enters the superconducting state below K. Moreover, KBi2 exhibits low critical fields in all measurements, field-induced crossover from second- to first-order phase transition in specific heat measurements, the typical magnetization isotherms of type-I superconductors, and a small Ginzburg–Landau parameter . These results clearly indicate that KBi2 is a type-I superconductor with a thermodynamic critical field Oe.