Epitaxial ferroelectric PbZrxTi1-xO3 (PZT) thin films have been deposited by pulsed laser deposition on LaAlO3 (001) substrates. The substrates were covered in situ with a thin SrTiO3 seed layer before the PZT deposition. Wide ranges of substrate temperature and oxygen partial pressure have been investigated in order to optimise structure and morphology. X-ray diffraction measurements revealed that epitaxial films with high crystalline quality were obtained at temperatures ranging from 600 degrees C to 750 degrees C and oxygen pressures from 0.03 to 0.2 mbar. Within this range, flat morphologies with rms roughness below 1 nm were observed by scanning electron and atomic force microscopies, whenever oxygen pressure was kept below 0.1 mbar and the films were 100 nm thick or less. A rougher columnar microstructure is obtained for thicker films and greater oxygen pressures. Ferroelectricity of the films has been tested in samples deposited on conductive SrRuO3 electrodes. Typical remanent polarisations of 13 mu C/cm(2) and coercive fields of 47 kV/cm are obtained.