The relation between the degree of entanglement and time scale of time-irreversible behavior is investigated for classically chaotic quantum coupled kicked rotors by comparing the entanglement entropy (EE) and the lifetime of correspondence with classical decay of correlation, which was recently introduced. Both increase on average drastically with a strong correlation when the strength of coupling between the kicked rotors exceeds a certain threshold. The EE shows an anomalously large fluctuation resembling a critical fluctuation around the threshold value of coupling strength where the entanglement sharply increases toward full entanglement. In this regime it can be shown that, although the correlation is hidden, EE and the lifetime of individual eigenfunctions also have a positive correlation that can be seen via an another measure.Introduction. -Classically chaotic quantum systems can be considered as the simplest systems exhibiting apparently time-irreversible behavior [1], and their quantum counterparts can also be the simplest systems realizing quantum irreversibility.Various examples of phenomena indicating evolution toward irreversibility, such as normal diffusion [2, 3], energy dissipation [4], energy spreading [5] and so on have been presented. Moreover, by coupling with a proper classically chaotic quantum system as a "quantum noise source", we can make a quantum system work as a quantum damper [6].However, quantum mechanical properties due to the quantum uncertainty principle prevent a quantum system from becoming irreversible in the same sense as its classical counterpart [2,3]. Indeed unbounded chaotic diffusion of a classical system is inhibited in its quantum counterpart. But if such systems are coupled even at classically negligible coupling strength, the diffusive motion exactly mimicking classical unbounded diffusion is recovered [7]. Such diffusive motion exhibits characteristics of