Optical microscopy of biological tissues at the 1700 nm window has enabled deeper penetration, due to the combined advantage of relatively small water absorption and tissue scattering at this wavelength. Compared with excitation at other wavelengths, such as the commonly used 800 nm window for two-photon microscopy, water absorption at the 1700 nm window is more than one order of magnitude higher. As a result, more temperature rise can be expected and can be potentially detrimental to biological tissues. Here, we present theoretical estimation of temper-ature rise at the focus of objective lens at the 1700 nm window, purely due to water absorption. Our calculated result shows that under realistic experimental conditions, temperature rise due to water absorption is still below 1 K and may not cause tissue damage during imaging.