The seed size and the substrate volume of containers can affect the quality of seedlings produced. The objective of this study was to evaluate the effect of seed size and substrate volume for seedling production on the emergence of Schizolobium parahyba seedlings (guapuruvu), initial growth, and dry mass accumulation of seedlings. Seeds were collected directly from the ground and were classified as small, medium, and large, being sown in containers with different substrate volumes (0.17 L, 0.34 L, and 0.75 L). The growth analysis and dry matter production were collected 14, 21, 28, and 35 days after sowing. The seed's water content of 4.14%. The smaller the seed size, the smaller their percentage and speed of emergence. There was no effect of substrate volume on seedling emergence, regardless of seed size. Seedlings' height, stem diameter, and dry matter increased linearly with time and substrate volume. With higher substrate volume and large seeds, S. parahyba seedlings have a higher emergence, initial growth, and dry matter production.