Abstract: The study evaluated the effect of Carya illinoinensis plant extracts on lettuce seed germination and development. Experiment was carried out in a completely randomized experimental design with five treatments and five replications. Plant extracts were prepared from the dry ground vegetable waste. The concentration was adjusted to 10% m.v-1. The treatments were classified into:heterogeneous pruning residues (HPR), leaves residues (LR), epicarp residues (ER), mesocarp residues (MR), and control treatment (CT, 100% water). The variables evaluated were:first germination count (GP4%), final germination count (GP7%), germination speed index (GSI), germination inhibition (PGI), frequency of abnormal seedlings (FAS), root length (RL), shoot length (SL), and total length of seedling (TLS). Extracts obtained from residues of C. illinoinensis decreased the lettuce seed germination, but their effect depends on the plant tissue (e.g. leaf, epicarp or mesocarp) used at production of plant extracts. Plant extracts from HPR and MR do not result in drastic allelochemical effects. Aqueous extracts from LR and ER reduced significantly the seed germination and the normal development of lettuce seedlings, with an absolute reduction in germination of 90.2% and 79.2%, respectively. Only plant extracts from leaf residues and epicarp residues from C. illinoinensis inhibit the germination and seedling development of L. sativa.