Orthorhombic TmMnO3 (o-TMO) thin films have been epitaxially stabilized on (110) SrTiO3 substrates by pulsed laser deposition (PLD) technique. The microstructure and strain relaxation mechanism of o-TMO thin films are analyzed using transmission electron microscopy. It is shown that major defects in the films are misfit dislocations with Burgers vectors of type a(p)< 010 > and a(p)< 110 >, whereas a(p) < 110 > dislocations tend to dissociate into partial dislocations with Burgers vectors of type 1/2a(p) < 110 >. Strain in o-TMO films is relaxed by misfit dislocations as well as surface fluctuations, which is different from most of the previous studies of the perovskite thin films. (C) 2011 Elsevier B.V. All rights reserved.