Composite materials exhibit many advantages over traditional materials and particularly in terms of lightness, mechanical resistance or chemical resistance. [1] The development of composites meets the requirements of industrial markets for applications in the fields of transport, construction, sports and leisure. In a context of sustainable development, a growing number of studies focus on the development of composites with biobased matrices. [2] Thus, polylactide (PLA) has become a major actor and could in the long term become an alternative to petroleum-based polyolefins. [3] Regarding the processes of composite manufacture, Resin Transfer Molding (RTM) is an innovative process based on the injection, in a mold containing fibers, of a monomer and a catalyst in order to carry out in-situ the polymerization of the matrix. [4] The major advantage over conventional melt processes is the access to high fiber content while improving their wetting by the matrix. Although a wide range of thermosetting matrix resins is available on the market, there are only few commercial resins for thermoplastic matrices. Regarding academic studies, composites based on poly(ε-caprolactone), were prepared [5], but no example was reported to date with lactide monomer. In order to design PLA-based composites by RTM, tin octoate was chosen as the catalyst as it displays some of the higest activity for the polymerization of lactide. [6] Polymerization tests were first tested at the lab scale before being upscaled in the RTM process. Poly(L-lactide) (PLLA)-based composites with glass fibers as reinforcement were obtained (figure 1). [7] The resulting PLLA matrix exhibits conversions up to 98 % along with high molar masses of up to 78,000 g.mol-1, when the polymerization is carried out under dynamic vacuum, with a good impregnation of the fibers by the matrix (figure 2).1. J-M. Berthelot, Composite Materials: Mechanical Behavior and Structural Analysis, 1st ed.; Springer: New York, USA; 1999, pp. 3-14.2. C. Baillie, Green Composites: Polymer Composites and the Environment, 1st ed.; Woodhead Publishing: Cambridge, England; 2004, pp. 1-8.3. M. Jamshidian, E. A. Tehrany, M. Imran, M. Jacquot, S. Desobry, Compr. Rev. Food. Sci. F., 2009, 9, 552. 4. K. Van Rijswijk, H. E. N. Bersee. Compos. Part A Appl. S., 2007, 38, 666. 5. (a) T.J.Corden, I.A.Jones, C.D.Rudd, P.Christian, S.Downes, Composites: Part A, 1991, 30, 737; (b) P. Christian, I. A. Jones, C. D. Rudd, R. I. Campbell, T. J. Corden, Composites: Part A, 2001, 32, 969. 6. H.R. Kricheldorf, I. Kreiser-Saunders, C. Boettcher, Polymer 1995, 36, 1253.7. E. Louisy, F. Samyn, S. Bourbigot, G. Fontaine, F. Bonnet, Polym. Bull. Under press.