A transient analysis of a single-effect LiBr-H2O absorption chiller taking into consideration the effects of thermal masses of main mechanical structures on heat transfer rate of low-pressure components and exergetic efficiency is achieved in this paper. The continuity of species constituting the LiBr-H2O solution, momentum equations and energy balances are solved simultaneously. Six various cases are considered to evaluate the effect of thermal masses of all and some components on the key parameters of an absorption chiller. To omit the numerical errors, thermodynamic properties are taken from the EES software. The fourth order Runge-Kutta method is selected to solve the simultaneous differential equations in MATLAB environment. The results show that the heat transfer rate of low-pressure components (absorber and evaporator) is hardly dependent of thermal masses of main components whereas the exergetic efficiency is highly affected by thermal masses.