The present research aims to study pollen grain and ovule development in Ageratum houstonianum. It can be suitable pattern for several species of capitule inflorescence, The flowers and buds in different developmental stages were removed, fixed in FAA70, stored in 70% ethanol, embedded in paraffin and sectioned with a thickness of 5-7 μm by microtome. Staining was carried out with Eosine and Hematoxylin. Then slides were studied using light microscope and were photographed. Results indicated that in bisexual florets, consist of five stamens with free filaments and apart from each other. Anthers are tetrasporangiated and development of anther wall is of dicotyledonus type and composed of one-layered epidermis, an endothecium, one middle layer and tapetum. the tapetum was plasmodial. Microspore tetrads are tetrahedral. Pollen grains are three colpated with echinated sculpturing, at the shedding time. Ovule was anatropous, unitegumic and tenuinucellate. Cell division of megaspore mother cells is of both longitudinal and transverse type and resulted to form linear or massive tetrads.The embryo sac development is of the polygonum type. Results of this research showed the presence of formed crystals in anther, the layer endothecium wall anther, epidermal cells of ovary, ovule, style, stigma and petal that was species specific characteristic. secretory (papillate) epidermis on the adaxial surface of petals, On the outer surface of petal long, filamentous and one-celled trichoms were visible.