There is provided an objective optical system for endoscope which is small-sized, and has a favorable optical performance and fast F-number.The objective optical system for endoscope is characterized by including a first lens L1 having a negative refractive power, a second meniscus lens L2 having a positive refractive power with a convex surface thereof directed toward the object side, an aperture stop S, a third lens L3 having a biconvex shape, and a cemented lens CL having a positive refractive power as a whole, in which a fourth lens L4 having a biconvex shape and a fifth lens L5 having a negative refractive power are cemented, andby satisfying the following conditional expressions (1) and (2) −3≤f1/Ih≤−1.2 0.25≤L3_5/L≤0.7 where,f1 denotes a focal length of the first lens L1Ih denotes the maximum image height of the objective optical system for endoscopeL3_5 denotes a distance along an optical axis AX from a surface on the object side of the third lens L3 up to a surface on an image side of the fifth lens L5, andL denotes a distance along the optical axis AX from a surface on the object side of the first lens L1 up to an image plane.
