Photothermal technology can be applied for thermal characterization of thin films and studying biological live cells. Using pulsed photothermal reflectance technique, thermal conductivity of thin films ranging from 20 nm to a few microns can be determined. Photothermal imaging (PTI) technique can provide ultra high spatial resolution and no fluorescence molecules are required. Comparison with normal phase contrast images, PT images reveal temperature distribution and more information on the intracellular components. Photothermal response (PTR) technique can provide high temporal resolutions. In monitoring the dying process of MDCK cells, significant changes in the PTR signals can be observed whereas unnoticeable changes are found in the images.