The influence of additional elements of aluminum alloy, especially of the elements other than conventional low melting point metals on machinability was investigated. Namely, the respective influences of Si, Ni, Mn and Fe on the machinability of AA6061 alloy used as base material were investigated. With the increase in the amount of each element the machinability of the alloy was improved. Si was the most effective among them, and Ni, Mn and Fe followed it in this order. It was found by microscopic observation that machinability was improved in proportion to the dispersion density of the second phase particles formed by the respective additional elements.