Morphogenetic alterations of rice spikelets grown under the influence of applied chemical hybridizing agent HGR-626 was studied using SEM and stereo microscope. Either a 10 ppm or 50 ppm solution of HGR 626 was sprayed at the spikelet primordium differentiation stage (Stage I), and in the middle of the meiosis stage (Stage II), respectively. Spikelets treated at Stage I showed such changes as: (1) spikelet and its component organs became smaller than control, (2) anthers of which bended toward axis, (3) no pollen mother cell differentiated in them, or (4) microspores with anther tissues ceased to develop, and, (5) exine of microspores developed irregularly to interconnect each other. Almost no content accumulated in them. On the contrary, 56.4% of pistils investigated in this study proliferated their ovaries and/or stigmata. Change of sex initiation namely pistil hyperplasia and stamen hypoplasia in rice spikelet as shown in this study indicated a similar tendency with the pistil hyperplasia and stamen hypoplasia induced by stressful environments studied previously. Skikelets treated at stage II showed no morphogenetic change as spikelets treated at stage I. This difference was considered to have occurred from the difference in developmental stage of apical meristem in spikelet primordia when the chemical was applied.