The recent discovery of superconductivity at 39 K in magnesium diboride, MgB2,  stimulated extensive research of this material's physical properties and future applications in superconducting electronics and optoelectronics. We report here our studies on optical photoresponse of superconducting MgB2 thin films using the femtosecond pump-probe spectroscopy [2,3]. In pump-probe experiments, the output of an ultrafast laser is divided into two beams. One beam is used to excite the sample. Since the pulse duration is only -100 fs, it acts as a delta-function-type excitation. The second beam probes the changes induced by the excitation, usually either as the relative change of reflectivity or transmissivity by as a function of the relative time delay to the pump beam. The probe beam is much weaker than the pump beam to ensure that the changes in the material are induced only by the pump beam. With femtosecond spectroscopy, we are able to study the dynamics of electrons and the electron-phonon interaction with subpicosecond resolution. In our experiments, a commercial Ti:Sapphire femtosecond laser with 76 MHz repetition rate is used to generate 100-fs-wide, 800-nm-wavelength optical pulses.