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Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ(LnBCO)single-crystalline thin films(Ln = Er,Pr; 0.0 < δ < 0.5)by carefully monitoring the resistance changes under a switching flow of oxidizing gas(O2)and reducing gas(H2)in the temperature range of 250~800 ℃.A giant resistance change ΔR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the ΔR vs.t plots,suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism.