An immersion microscope objective comprises, in order from an object side, a first lens group having a positive refractive power comprising a cemented lens composed of a plano-convex lens whose plane surface faces the object side and a meniscus lens whose concave surface faces the object side, and at least one single lens having a positive refractive power; a second lens group having a positive refractive power comprising a three-piece cemented lens; and a third lens group having a negative refractive power including a Gaussian type lens structure, wherein the objective satisfies the following conditions when n1, NAob, d0 and β are a refractive index at a d-line of the single lens having the highest refractive index included in the first lens group, a numerical aperture on the object side of the objective, a working distance of the objective, and a magnification of the objective, respectively. 1.7≦n1 0.75≦NAob≦1.45 0.4≦NAob*d0≦3 0.03≦NAob/β≦0.1.