In cutting aluminum alloy 6061, continuous chips have a negative influence on the machining operation. Usually, Pb is added in order to break continuous chips. However, from the standpoint of environmental protection, it is necessary to improve chip breakability without adding Pb. One effective measure is improving chip breakability by adding Si in aluminum alloy 6061. However, the influence of Si content on tool wear has not been fully examined. In this study, in order to clarify the influence of a diamond-like carbon (DLC) coating layer on cutting performance, aluminum alloys having different Si contents were turned. The substrate of the tool material was high speed steel (1.4%C). The chip configuration, cutting force and tool wear were experimentally investigated. The following results were obtained: (1) The DLC coating layer was effective for decreasing the cutting force. (2) In cutting Al-2mass%Si alloy, the wear progress of the DLC-coated tool was slower than that of the un-coated tool. The length of a chip with the DLC-coated tool was shorter than that with the un-coated tool.