Ultra-small, 1.8-2.3 nm, CdS quantum dots (QDs) stabilized by polyethyleneimine (PEI) in water and guanidine dendrimers in dimethylformamide were prepared. CdS-PEI QDs have narrow size distribution of around 10% and photoluminescence emitted in a broad range of 400-600 nm with the quantum yields of 10-20%. Photoluminescence decay kinetics of CdS-PEI QDs is very non-exponential with an average radiative life time growing from ~15 to ~80 ns with the light quantum energy varying from ~3.2 to ~1.8 eV. Vibrational Raman spectra of CdS-PEI QDs exhibit a main peak at 250-300 cm- 1 which is a superposition of longitudinal, transverse and surface-related vibrational modes, broadened due to spatial phonon confinement and structural reconstruction of QDs. Dendrimer-stabilized CdS QDs emit electroluminescence in the range of 450-700 nm under applied voltage higher than 6 V. Unusually strong temperature dependences of photoluminescence intensity and spectral maximum energy of CdS-PEI QDs in aqueous solutions and PEI films in the range of 280-353 - were found and interpreted in terms of reversible dissociation of a PEI complex with under-coordinated Cd(II) atoms on the QD surface.