  We have grown MgB2 films in a postannealing process. Precursors were prepared
on Al2O3(0001) substrates by codeposition of Mg and MgB2 using pulsed laser
deposition technique. Superconducting MgB2 thin films were obtained via an ex
situ postannealing process, with various annealing temperatures and durations.
In magnetic measurement we found more than one transitions in almost all the
samples, and the temperature dependence of the resistance confirmed this
phenomena. We proved this is not result of magnesium deficiency. Transportation
properties of MgB2 thin films under strong magnetic fields are also studied.
