Abstract: Based on selective laser melting (SLM) method, Al matrix composites reinforced with various mass fraction of carbon nanotubes(CNTs, mass fractions were 0, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, respectively) were produced by changing scanning speed. The effect of CNTs content and laser scan speed on performance of Al matrix composites was investigated. The results show that the dispersion is better and most of CNTs adhere to the surface of Al powder in a single state when the CNTs content(mass fraction)is not more than 1.0wt%, while the number and size of CNTs agglomerations are enhanced when the CNTs content exceeds 1.0wt%. Under the same SLM process condition, the number of pores in CNTs/Al composite specimens at low CNTs content is less so that relative densities are high. At high CNTs content, porosity of CNTs/Al composite specimen increases and relative densities of specimens reduce. With the CNTs content rising, hardness of CNTs/Al composite specimen increases firstly and then decreases at scanning speed of 1 300 mm/s. The micro-hardness of CNTs/Al composite specimen at the CNTs content of 1.0wt% reaches the peak. Compared with aluminum alloy specimen, CNTs/Al composite specimen shows finer grain size. The hardness of CNTs/Al composite specimen that the CNTs content is exceeding 1.0wt% decreases due to lower relative density, though grain size demonstrates the fine tendency.