The temperature of metastable chlorine ions Cl+* in a time-modulated inductively coupled plasma was measured with the time-resolved laser-induced fluorescence technique. The Cl+* temperature changed periodically according to the modulation of the plasma and decreased slightly in the afterglow region. The Cl+* temperature was measured as a function of rf power and gas pressure, while the relative Cl+* density was also measured simultaneously as a function of time. The Cl+* density decreased to be 30% of the maximum density within 10 mu s in the discharge-off periods.