Semiconductor surfaces are easily oxidized by exposure to air for extended period of time. In this work we want to examine the change of series resistance and conductance of Cu/n-Si Schottky diode upon being exposed to air. We studied the effects of native oxide layer on current-voltage ($I$-$V$), capacitance-voltage ($C$-$V$), conductance-voltage ($G/\omega$-$V$) and conductance-frequency ($G/\omega$-$f$) characteristics of Cu/n-Si Schottky diode. For this aim, we fabricated one reference diode and five Cu/n-Si diodes exposed to air for extended period of time. From $I$-$V$ plot of the Cu/n-Si/Al diodes ideality factor ($n$), saturation current ($I_0$) have been calculated. Barrier height ($e\Phi_b$) and series resistance ($R_S$) have been calculated by using Norde functions. $C$-$V$, $G/\omega$-$V$ and $G/\omega$-$f$ characteristics of diodes have been examined. The obtained results show that native oxide layer have an important effect on the values of series resistance, barrier height, ideality factor and conductance of studied diodes. The value of ideality factor and series resistance increased with time of exposure to air, while the barrier height $e\Phi_b$ values of air-exposed Schottky diode is smaller than that of the reference diode. The differences of series resistances between reference diode and air-exposed diodes are high while within air-exposed group small differences of series resistance are observed.