Streptomyces chusanensis ZS-2, isolated from a soil sample in Chusan in Taiwan, was found to produce a new Type II restriction endonuclease. This restriction enzyme was designated as SchI. The purified enzyme was characterized as having a subunit mol wt of 28 kDa, and was apparently free from exonuclease activities. It cleaves the phosphodiester bond between the fourth C and the fifth G on the 5'-CCGCGG-3' sequence of DNAs, leaving a 2-nucleotide protruding end at its 3' site. This data suggests that SchI is an isoschizomer of SacII. Ln addition, based on the comparison between SchI and SacII regarding reaction parameters, it seems that SchI is a better choice of restriction enzyme for genetic analysis and mapping.