FOSS (Free and Open Source Software) is repeatedly modified and reused by other FOSS or proprietary software systems. They are released to others under specific licenses whose terms and conditions are usually written on the source-code files as program comments. There are a few researches which automatically analyze the licenses in a FOSS release, but there is no statistical study on the evolution of licenses along the evolution of FOSS. In this paper, we analyze licenses through FreeBSD, OpenBSD, Eclipse, and ArgoUML evolution, using our license analysis tool Ninka, and discuss characteristics on the evolution of the license used in those systems.