  We present experimental results of the upper critical fields $H_{\rm c2}$ of
various MgB$_2$ thin films prepared by the molecular beam epitaxy,
multiple-targets sputtering, and co-evaporation deposition apparatus.
Experimental data of the $H_{\rm c2}(T)$ are successfully analyzed by applying
the Gurevich theory of dirty two-band superconductivity in the case of
$D_{\pi}/D_{\sigma}>1$, where $D_{\pi}$ and $D_{\sigma}$ are the intraband
electron diffusivities for $\pi$ and $\sigma$ bands, respectively. We find that
the parameters obtained from the analysis are strongly correlated to the
superconducting transition temperature $T_{\rm c}$ of the films. We also
discuss the anormalous narrowing of the transition width at intermediate
temperatures confirmed by the magnetoresistance measurements.
