The layered MoS2 has recently attracted significant attention for its excellent nonlinear optical properties.Here,the ultrafast nonlinear optical (NLO) absorption and excited carrier dynamics of layered MoS2 (monolayer,3-4 layers,and 6-8 layers) are investigated via Z-scan and transient absorption spectra.Our experimental results reveal that NLO absorption coefficients of these MoS2 increase from-27×103cm/GW to-11 × 103cm/GW with more layers at 400-nm laser excitation,while the values decrease from 2.0 × 103 cm/GW to 0.8 × 103 cm/GW at 800nm.In addition,at high pump fluence,when the NLO response occurs,the results show that not only the reformation of the excitonic bands,but also the recovery time of NLO response decreases from 150ps to 100ps with an increasing number of layers,while the reductive energy of A excitonic band decreases from 191.7meV to 51.1meV.The intriguing NLO response of MoS2 provides excellent potentials for the next-generation optoelectronic and photonic devices.