In assessing the quality of drinking water in transmission and distribution lines, the study on chlorine reactions is of particular importance. Chlorine decay happens in bulk and wall and it is mainly affected by the water age which depends on the transmission line length. Residual chlorine concentration in Isfahan water transmission line (IWTL) is simulated through three decay models, namely the first order, parallel first order and second order single reactant (SR model) which incorporated in EPANET and EPANET MSX, respectively. The results of the models are compared through two approaches, one is the one-part approach (OPA) whereby chlorine decay simulation is performed taking into account the whole line as one section and the second is multi-part approach (MPA) whereby the line is divided into two sections and decay coefficients of chlorine for each section are separately determined. Results show that in the OPA, the SR model in summer and the parallel model in winter are the best kinetic models. While in the MPA, the results of first order model has the same order of accuracy as the more complex models of parallel and SR models. In general, the simple first order model in the MPA applied by EPANET2.0 s/w provides acceptable level of accuracy in compare to the complex models applied in EPANET MSX s/w. The average RMSE volumes are reduced from 0.078 in OPA to 0.029 in MPA in summer and from 0.059 to 0.015 in winter, indicating that the dividing the line in simulation procedure and considering the individual decay coefficient for each part, considerably improves the results, more effectively than the application of advanced decay models.