Nanotetrapods of alloy CdS1-xSex and core-shell (CdS)(1-x)@(CdSe)(x) are fabricated easily in water using ethylenediamine as a solvent-coordinating molecular template, and then their optical properties are investigated using diverse static and time-resolved spectroscopic methods. The arms of the alloy nanotetrapods have single-crystalline structures of CdS1-xSex without showing staking faults, while the arms of the core-shell nanotetrapods display polycrystalline shell structures of CdSe. The optical properties of CdS1-xSex, where Se atoms are isolated in the CdS lattice, are very different from those of (CdS)(1-x)@(CdSe)(x) where banded CdSe passivates the CdS core. Compared with pure CdS nanotetrapods, the photoluminescence of CdS0.9Se0.1 shifts to the red by 40 nm, whereas that of (CdS)(0.9)@(CdSe)(0.1) does so only by 5 nm. Although the mean luminescence lifetime of alloy CdS1-xSex is shorter than that of pure CdS, it is still much longer that that of core-shell (CdS)(1-x)@(CdSe)(x).