Femtosecond pump-probe experiments in a transmission geometry were performed on Sn-doped n-type beta-Ga2O3. With the pump and probe wavelengths below the bandgap, the differential transmission signal was determined by the free electron dynamics. Differential transmission decay times and their spectral dependence were used to evaluate electron-phonon scattering for polar optical (PO) and intervalley phonons. The obtained average electron-PO phonon scattering time is 4.5 +/- 0.4fs, while the electron scattering to and from the side valley is 80 +/- 5 fs. The energy between the absolute and second lowest conduction band minima is estimated to be 2.6 +/- 0.1eV.