The occurrence of the solitary ascidian Ciona savignyi Herdman, 1882 in Vostok Bay (Peter the Great Bay, Sea of Japan) was first documented in 2004. Adult specimens occurred in fouling communities of floating docks in Gaidamak Bay and on different anthropogenic substrates. The introduction of this ascidian into Vostok Bay is attributable to fishing ships which regularly frequent ports of Japan and to favorable environmental conditions (temperature and salinity of seawater).