IrO2 thin films were prepared on Si (100) substrates by pulsed laser deposition (PLD) technique. Emphases were given on the variation of the electrical resistivity and microstructure of IrO2 thin films before and after being annealed at air atmosphere. The composition and microstructure of IrO2 thin films were characterized by using x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and the four-point probe method was used to measure their electrical resistivity. Hall measurements were used to study the electrical mechanism of IrO2 films. The results show that the annealing in air could improve the conductivity of IrO2 films, and the minimum electrical resistivity of 37 μΩ·cm is obtained at 750 °C. IrO2 films had a significant positive temperature dependence of resistivity at 25-500 °C, showing a typical metallic conduction behavior. It is found that IrO2 films deposited at the substrate temperature of 250-400 °C exhibited p-type conduction, while the conductivity type changed to n-type when the temperature increased to above 500 °C.