In this study, 1T phase molybdenum disulfide Ultra-thin Flakes (1T-MoS2 UFs) with high HER activity was successfully prepared by spatial confinement of layered double hydroxides (LDHs). The growth of MoS2 tends to be thin layer and high 1T phase due to the binding force of LDHs, this novel strategy is different from other phase transition methods, like alkali metal ion intercalation, electron irradiation, and stress induction, etc. The 1T-MoS2 UFs were used as hydrogen evolution reaction (HER) catalysts, when current density is 10 mA/cm(2), the potential (vs. RHE) is 254 mV and the Tafel slope is only 64 mV/dec under the optimal condition. The superior HER activity is due to highly active 1T phase and rich defects. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.