The structure of cadmium sulfide (CdS) micelle in stable aqueous solution of ethylenedi aminetetraacetic acid was determined by dynamic light scattering, small angle X ray scattering and neutron scattering. The micelle aggregate is a single CdS nanoparticle with an average size of about 3 nm, the nanoparticle organic shell and the solvation shell are about 1 nm and 5 nm thick, respectively. These parameters were confirmed by the scanning semi contact atomic force microscopy and powder X ray diffraction studies of dry micelle cores isolated by high speed centrifugation. The CdS micelle was correctly described by a simple double shell model and was found to possess the structure corresponding to CdS quantum dots.Key words: cadmium sulfide, chemical condensation from aqueous solutions, micelle structure.Cadmium sulfide (CdS) nanoparticles and quantum dots (QD) are intensively studied because they possess unique catalytic and luminescent properties. 1-4 Cadmi um sulfide nanoparticles which are slightly larger in size than the exciton Bohr radius (3 nm) can be used in cataly sis for production of hydrogen, 5,6 for the purification of water from organic impurities, 7,8 and in organic syn thesis. 9 Cadmium sulfide nanoparticles whose size is equal or smaller than the exciton Bohr radius in bulk CdS, i.e., CdS QD, are a promising material for the design of robust fluorescent biosensors, 10,11 solar cells, 12 and lasers. 13 In the last twenty five years, procedures for the syn thesis of nanoparticles and colloidal QD were developed for many chalcogenides. The results on the synthesis of CdS nanoparticles and QD with various sizes and proper ties can be found in the literature. 14-21 The main restrain ing factor for the fundamental studies and practical appli cation of CdS nanoparticles is the toxicity of both cad mium ions 22,23 and organic compounds used presently for the synthesis and stabilization of nanoparticles. 17,20 Replacement of cadmium by nontoxic zinc, though being attractive for environmental reasons, has a fundamental disadvantage related to a too wide forbidden band of zinc sulfide (3.68 eV); the blue shift can only broaden it. 24 This leads to a shift of the absorption band to the UV region. Therefore, QD based on zinc sulfide cannot be used in many topical applications dealing with biology, medicine, and visible light photocatalysis. Replacement of CdS by silver and tin sulfides having narrower forbidden band is principally possible, but requires conducting of expensive preliminary quests and searches. However, all the alterna tive metals considered do not solve another important problem, viz., the toxicity of the organic stabilizing media.A possible way to solve this problem is to synthesize nanoparticles in nontoxic aqueous media. However, CdS is a hydrophobic compound; therefore, its synthesis di rectly in the aqueous solution is accompanied by intense agglomeration. These processes lead not only to coagula tion (sticking together), but also coalescence (a multiple increase in size) of nanoparticles. ...