In general, for polymeric materials, the effects of orientation on physical properties are strongly relevant: for instance, the extent to which it is possible to increase stiffness and strength find no parallel with other materials. 1 Moreover, crystalline phase orientation is particularly relevant for functional polymeric materials, when the functionality is mainly associated with crystalline phases, as for conductive 2 or ferroelectric 3 polymers. Generally for macroscopic semicrystalline polymers, uniplanar orientations are achieved only as a consequence of (mainly biaxial) mechanical stretching. The easy achievement of uniplanar orientation, without mechanical stretching, has been observed so far, by co-crystallization of syndiotactic polystyrene (s-PS) 4 and poly(2,6-dimethyl-1,4-phenylene ether) (PPO) 5 with different low-molecular-mass guest molecules. In this communication, we present the possibility to achieve uniplanar orientation, in the absence of mechanical stretching, for poly(L-lactic acid) (PLLA) 6 i.e. another industrially relevant semicrystalline polymer, which is able to co-crystallize with many guest molecules. 7 These recently results let us to suggest that polymer co-crystallization could be a general route for getting uniplanar orientation, without mechanical stretching, in polymeric thick films. Keywords: Guest induced crystallization, Thick polymeric films, Crystalline phase orientation References [1] I. M. Ward, In Structured and properties of Oriented Polymers, Chapman & Hall, London, (1975); Chapter 1, p. 1. [2] M. Yoshio, T. Kagata, K. Hoshino, T. Mukai, H. Ohno, T. Kato, J.Amer.Chem.Soc. 128 (2006) 5570 [3] Z.Hu, M. Tian, B. Nysten, A.M. Jonas, Nature Mater. 8 (2009) 62 [4] G. Guerra, C. Daniel, P. Rizzo, O. Tarallo, J. Polym. Sci. Polym. Phys. Ed. 50 (2012), 305 [5] P. Rizzo, G. Ianniello, S. Longo, G. Guerra, Macromolecules 46 (2013) 3995 [6] P. Rizzo, G. Ianniello, V. Venditto, O.Tarallo, Macromolecules (2015) submitted [7] H. Marubayashi, S. Asai, M. Sumita, Macromolecules 45 (2012)1384.