The ultrafast dynamics of chlorobenzene clusters upon 271 nm excitation is studied by femtosecond pump-probe time-of-flight mass spectrometry. Transient profiles of clusters are fitted by two-exponential decay component models, an ultrafast component and a slow decay component. The ultrafast (similar to 170 fs) decay of S-1 state is tentatively attributed to the internal conversion to the high vibrational levels of S-0 state. Lifetimes of this ultrafast component decease with the cluster size, due to the influence of the solvation effects, while lifetimes of the slow decay component (>1 ns) increase with the cluster size, due to the increase of freedom degrees. (C) 2009 Elsevier B. V. All rights reserved.