A pot culture experiment was conducted in the nursery of Department of Silviculture, Forest College and Research Institute, Tamil Nadu Agricultural University, Mettupalayam, Tamil Nadu during summer season (February - April) 2016, to study the allelopathic effect of Lantana camara (L.) and Parthenium hysterophorus (L.) on germination and growth of Thespesia populnea (L.) tree species under greenhouse condition. Aqueous extracts of L. camara and P. hysterophorus at four concentration levels viz. 10, 20, 30 and 40% with absolute control (distilled water) were assigned as experimental treatments under completely randomized design and replicated thrice. Application of whole plant aqueous extract of P. hysterophorus and L. camara at 40% concentration recorded lower seed germination of 26.7% and 36.7% and germination value of 3.0 and 5.2 respectively than application of aqueous extracts of the weeds at 30, 20 and 10% concentration levels. Application of P. hysterophorus weed extract at 40% concentration recorded higher inhibition of shoot growth, root growth, total length and dry matter production of T. populnea seedlings than its application at lower concentrations and over L. camara weed extract at all concentrations.