In order to observe the infrared spectrum of OCSe, a sufficient amount was readily synthesized by using a heat pipe reactor. Thirteen vibrational bands were observed in the region of 400 ∼ 4000 cm −1, seven of which have never been reported. The high-resolution FTIR spectrum of the 2 ν 1 band of OCSe was recorded with a resolution of 0.005 cm −1. Analysis provided molecular constants for the 2 ν 1 band of 16O 12C 80Se and 16O 12C 78Se in natural abundance.