Resumo. The dimensions of the container affect both the production cost and the quality of seedlings of forest species, and the pattern of response of these depends on the specificity of the species. The objective of this study was to evaluate the effect of size of containers on the initial growth of forest species Mezilaurus itauba Taub. ex Mez and Platymiscium ulei Harms. Two experiments were conducted concomitantly in nursery conditions, using the completely randomized design with five replicates. The treatments comprised of six sizes of containers: 20 cm x 15 cm (T1), 20 cm x 20 cm (T2), 23 cm x 20 cm (T3), 25 cm x 20 cm (T4), 30 cm x 20 cm (T5) and 33 cm x 23 cm (T6). After 90 days of growth, the size of containers affects differently the quality of the seedlings of both the species. The size of container 25 x 20 cm is more appropriate for the cultivation of macacaúba species while the best response to itaúba was obtained for the container 33 x 23 cm. On the other hand, the containers 20 x 15 cm and 20 x 20 cm should not be used for any of the tested species.