Size and shape controlled semiconductor nanocrystals have been synthesized via a molecular precursor approach using single source precursors, $Zn(EPh)_2$(TMEDA) (E= Se, Te and TMEDA= N,N,N`,N`-tetramethylethylenediamine), which is effectively utilized for the synthesis of semiconductor nanocrystals by a thermolysis process. Sizes of obtained nanocrystals are precisely tuned depending on growth temperature and the shape of the nanocrystals varies from 0-dimensional nanocrystals to 1-dimensional nanorods depending on growth condition. Obtained nanocrystals show quantum confinement effects and their optical properties such as absorption and luminescence are shifted to higher energies depending on the crystal size when compared to bulk materials. This study demonstrates utilization of molecular precursors as a facile method for size and shape controlled synthesis of the semiconductor nanocrystals. This approach can lead to the formation of many interesting new nanostructured materials.