We have recently succeeded in preparingb‐axis oriented YBa2Cu3Oythin films by laser metalorganic chemical vapor deposition and special thermal treatments. Theb‐axis orientation means that the CuO chain in the basal plane is perpendicular to the film surface, while thea‐axis orientation is parallel to the film surface. When oxygen is introduced after complete oxygen depletion aroundy≊6, we always obtaina‐axis oriented films. On the other hand,b‐axis oriented films can be obtained if the film whosec‐axis is parallel to the film surface is refilled with oxygen after medium oxygen reduction close to the orthorhombic‐tetragonal phase boundary. These phenomena can be explained by oxygen arrangement in Cu‐O basal planes caused by the stress between the deposited films and the substrates due to the difference in their thermal expansion coefficients. ©1995 American Institute of Physics.