Superconducting Y1Ba2Cu3O7−δ films were prepared on the MgO (100) and SrTiO3 (100) single crystals using metal organic chemical vapor deposition (MOCVD) of β-diketone metal chelates of Y(thd)3, Ba(th)2, and Cu(thd)2. The evaporation kinetics of Y(thd)3, Ba(thd)2, and Cu(thd)2 and the ratios of deposited to evaporated mole percents of Y, Ba, and Cu cations were studied. The microstructure of Y1Ba2Cu3O7−δ films deposited using MOCVD was observed using scanning electron microscopy and transmission electron microscopy to investigate surface morphology change with the film composition and transformation twin structures. The experimental results showed that the volatility of Ba(thd)2 did not perceptively increase with decreasing evaporation pressure from 10 Torr to 5 Torr, but that of Y(thd)3 or Cu(thd)2 increased with the pressure decrease. The ratio of deposited to evaporated mole percents of Ba cation was smaller than those of Y and Cu cations. Therefore, Ba must be evaporated more than the stoichiometric amount for Y1Ba2Cu3O7−δ in order to obtain single phase Y1Ba2Cu3O7−δ films. The surface morphology of the Y1Ba2Cu3O7−δ films showed perculiar changes with slight composition changes. The transition onset and zero resistance temperatures of typical stoichiometric film deposited on MgO were 93 K and 91 K, respectively. The Y1Ba2Cu3O7−δ films had about 50 nm grain size, and most grains consisted of transformation twins. The critical current density of a film deposited on SrTiO3 was 105 A/cm2 at 77 K and zero magnetic field.