A thin photothermal (PT) endoscope (∼80 μm ) for the noninvasive/minimally invasive hybrid-optical diagnosis of biological specimens is demonstrated. The technique has the unique advantage that the pump laser delivery fiber itself acts as the thermal wave sensor, which is a Bragg grating. It detects only the conductive component of the PT signal, thus enabling an emissivity independent measurement. The device is slidable through a syringe needle and PT analysis of exposed organs with limited accessibility for conventional PT techniques, and constricted regions can be examined noninvasively. For regions buried in thick tissues, a minimally invasive injection mode may be considered. Temperature measurement sensitivity is about 0.03°C. The amplitude and phase channels are sensitive up to about 3 and 10 kHz, respectively. The endoscope has been used for the simultaneous estimation of flow velocity, absorption coefficient, and diffusivity for a phantom-blood flow. The endoscopically estimated values are in agreement with true flow velocities over a range of 1 to 1000 cm −1 . The endoscope has been used for the optical biopsy of goat bone marrow.