We present a rigid miniaturized optical system block fiber-optic two-photon endoscope based on a compact two-axis piezo scanner system and a miniature high (0.65) NA GRIN lens objective. The optical system is scanned as a whole by a piezo scanner allowing always an on-axis beam irradiation of the optical system. A photonic crystal fiber is used for excitation and ultrashort laser pulses can be delivered with typical power up to $100\mathrm{mW}$ at $800\mathrm{nm}$ . Two-photon fluorescence signal is collected by the use of a multimode fiber. Lateral resolution values for the system were experimentally measured to be $0.67\mathrm{\mu m}$ vertically and $1.08\mathrm{\mu m}$ horizontally. Axial resolution was found to be $5.8\mathrm{\mu m}$ . The endoscope is highly flexible and controllable in terms of time acquisition, resolution, and magnification. Fluorescence images were acquired over a $420\mathrm{\mu m}\times 420\mathrm{\mu m}$ field of view. Results presented here demonstrate the ability of the system to resolve subcellular details and the potential of the technology for in vivo applications.