It is important to accelerate the development of the laser welding technology of marine high strength steel E36. Laser butt welding of 3.2-mm thick E36 is performed by using a YbYAG laser. The microstructure and hardness of weld joints are analysed and the effects of the welding speed on properties of the weld joints are studied. The result shows that the microstructure of weld zone (WZ) is mainly martensite, and the microhardness of WZ is higher than that of base metal (BM). The hardness distribution of weld joint is non-uniform. The weld edge has an highest hardness. Heat affected zone (HAZ) is very narrow and the hardness in this zone drops quickly. With the increase of the welding speed, the properties and microhardness also change: When the welding speed is 70 mm/s, the highest hardness of the WZ is 448.9 HV, which is the highest of all the samples, and the hardness in its HAZ drops most quickly. The tensile samples which are welded at speed from 20 mm/s to 60 mm/s are all broken in base metal. When the welding speed is 70mm/s, the samples are all broken in fusion line and its ductility is obviously worse than that broken in base metal.