A large magnetoresistance change (ΔR/RH) of −550% has been observed at 270 K in (La0.8Ca0.2)MnO3 thin films. The films were prepared in situ on LaAlO3 substrates by single-liquid-source metal-organic chemical vapor deposition. M(thd)n (M = La, Ca, and Mn, and n = 2, 3) were dissolved together in an organic solution and used as precursors for the deposition of (La0.8Ca0.2)MnO3 thin films. Deposition was conducted at an oxygen partial pressure of 1.2 Torr and a substrate temperature ranging from 600 °C to 700 °C. The mechanism for the large magnetoresistance change in this manganese oxide is briefly discussed.