We correlated the crystallinity of YBaCuO films prepared by magnetron sputtering deposition using Ar/O(2) mixture gas with the atomic and molecular composition in the gas phase. YBaCuO films were deposited on MgO substrates at 670 degrees C. Two-dimensional distributions of Y, Ba, Cu, YO, BaO, and CuO densities and one-dimensional distribution of O density were measured by laser-induced fluorescence spectroscopy. The Y and Ba densities decreased significantly with the increase of the O(2) partial pressure, and they were below the detection limit at an O(2) flow ratio of 10% and a total gas pressure of 53 Pa. The decrease in the Y and Ba densities was compensated by an increase in the YO and BaO densities. The decrease in the Cu density with the increase of the O(2) partial pressure was less significant, while the CuO density was below the detection limit at all the discharge conditions. The O density was evaluated to be 10(12)-10(11) cm(-3), which was much higher than the Cu density. On the other hand, YBaCuO films with high crystallinity were obtained at total gas pressures of 53-80 Pa and O(2) flow ratios of 50-70%. Therefore, it is concluded that the precursors for the deposition of YBaCuO films with high crystallinity are Cu, YO, BaO, and O. (C) 2008 Elsevier B.V. All rights reserved.