While simultaneous phase-contrast and two-photon fluorescence imaging in microscopy can bring abundant biomedical information, it is difficult to retrieve phase information from conventional two-photon microscopes. To realize low-cost, in situ phase-contrast and two-photon fluorescence imaging, we propose Schlieren two-photon microscopy, a method that implements phase-contrast imaging on two-photon microscopes. This method involves spatially modulated fluorescence plates, which are made of two-photon fluorescence dyes or upconversion nanoparticles. We demonstrate that the fluorescence intensity fluctuation reflects the phase gradients of the specimen via theoretical analysis, simulations, and experiments. The proposed method is fully compatible with commercial two-photon microscopes, thus enabling widespread applications in live tissue imaging.