The microstructure of the outgrowths on the surface of pulsed laser ablated YBa 2 Cu 3 O 7 (YBCO) thin films deposited on (100) Y stabilized zirconia substrates was studied by transmission electron microscopy. The outgrowths consist of misaligned superconducting c-axis YBCO grains and a-axis YBCO grains, non-superconducting CuO, Ba 2 CuO 3 , BaCuO 2 , CuYO 2 and Y 2 BaCuO 5 grains about 0.1-5 μm in size. The Y-123 type outgrowths are block-shaped misaligned with the YBCO matrix The non-superconducting grains mostly are semi-spherical in shape and have a certain crystallographic relation with the YBCO matrix. The protruding heights of the outgrowths on the surface of the film are about 50-450 nm.