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.
