High transition temperatures into superconducting state of the iron-based chalcogenides have attracted particular attention due to promising applications. Early, it was suggested that the ground state and Tc of the RbxFe2-ySe2 system can be changed by thermal treatment [1,2].  Here we carried out an extended study of thermally treated single crystalline samples of Rb0.8Fe1.6Se2-zSz system with z substitution between 0 and 2. The single crystals of the anion-substituted Rb0.8Fe1.6Se2-zSz have been grown by the Bridgman method. In order to study the thermal evolution of phase separation, single crystals were characterized by differential scanning calorimetry (DSC). Thermal measurements were performed with a Perkin Elmer DSC 8500 system, by heating up and cooling down in a temperature range from 420 K to 600 K, with a constant heating rate of 5 K/min.  Figure 1 presents the phase diagram for Rb0.8Fe1.6Se2-zSz system for the whole substitution range z (0 ≤ z ≤ 2) which includes transition temperature into superconducting state (SC) (Tc), temperature of the antiferromagnetic ordering (TN) and temperature of the vacancy ordering (Ts). The values of Tc were determined from the magnetic measurements. A continuous reduction of the Tc with increasing the substitution from 0 to 1.1 was observed. The inspection of differential scanning calorimetry signal reveals several phase transformations: structural transition at Ts at which the structure transforms from high-temperature I4/mmm structure into a low-temperature superstructure I4/m) and transition at TN with long-range antiferromagnetic order (AFM). Both, heating and cooling reveals nearly the same DSC behavior with substitution z. In addition, at a substitution range between 1.1 and 1.2, region attributed to a suppression of the superconducting state, transitions at Ts and TN show significant modification. In some samples, the third anomaly in DSC curves was detected which is associated with the phase separation transition at Tp.