This study aimed to evaluate the allelopathic effects of aqueous extracts of Tectona grandis L.F. in various concentrations produced from leaves and flowers. Seeds of lettuce (Lactuca sativa L.) and germitest paper as substrate were used, the germitest paper was moistened with distilled water, and aqueous extract in concentrations of 100%, 75%, 50%, 25% and 0% (distilled water). The extracts were homogeneously deposited on twenty-five seeds evenly distributed in gerbox-type boxes. The materials used in the experiment were previously sterilized with alcohol (70%). A completely randomized experimental design with four replicates was used and the experiment was conducted under natural conditions of temperature and humidity. The tests were carried out in the laboratory, the experiment was watched for 10 days always at the same hour and the variables analyzed were Germination Percentage (%G), Speed of Germination Index (SGI), Mean germination time (MGT) and Mean speed of germination (MSG). The data were submitted to Analysis of Variance and compared by Tukey test considering 95% of probability. It was observed that there were no significant differences in leaf and flower extracts for the variables %G, MGT and MSG, however, in SGI aqueous leaf extract differed significantly at the highest concentrations (75% and 100%). It was concluded that aqueous extracts of leaves and flowers of T. grandis had no inhibitory potential in relation to the percentage and average germination time of lettuce seeds at any of the concentrations.