Provided is an immersion oil for microscope including a liquid olefin polymer (A), a liquid diene polymer (B), a diaryl alkane (C), and an alkyl benzene (D), the immersion oil for microscope being capable of maintaining low fluorescence of its own over a long period of time, having good characteristics required for an immersion oil for microscope, such as good refractive index, Abbe number, viscosity, and resolution, and being particularly suitable as an immersion oil for a fluorescence microscope.