Heterostructure MoS2 nanosheets decorated CdS nanoparticles were successfully prepared by a facile two-step solvothermal method. The growth of ultrathin MoS2 nanosheets on CdS surface in terms of thickness and interlayers of (002) MoS2 was controlled by changing solvothermal reaction temperature. A series of MoS2 nanosheets decorated CdS nanoparticles were prepared at different temperature. The synthesized composites were characterized with XRD, FESEM, TEM, UV-vis DRS, BET, PL, XPS, EPR and I-T. TEM observations revealed the growth of ultrathin MoS2 nanosheets over the CdS nanoparticles, the thickness of MoS2 sheets and interlayers distance of (002) in composite was found to decrease with increasing the reaction temperature to 220 degrees C, under the same conditions. Photocatalytic activities of the as-prepared MoS2/CdS nanocomposites for the MO degradation were evaluated under the visible light irradiation. The ultrathin MoS2/CdS nanocomposites 1-220 with thinner sheets prepared at 220 degrees C exhibits higher photocatalytic efficiency for degradation of MO under visible light than all the other synthesized samples at different temperature. Furthermore, it was found that this catalyst retains remarkable photocatalytic activity after five cycles. The PL spectrum and photocurrent responses results suggest that the MoS2/CdS nanocomposite 1-220 possess higher separation efficiency and minimum recombination of photo-generated electrons and holes than pure CdS. The photocatalytic degradation mechanism of the MO over MoS2/CdS nanocomposite was proposed.