Potentially toxic diatoms Pseudo-nitzschia calliantha and P. fraudulenta were found in bottle samples of phytoplankton collected in Amurskii Bay (East/Japan Sea) and in the coastal waters of Sakhalin Island (East/Japan Sea and Sea of Okhotsk) in different seasons during 2002-2006. The mass development of these species occurred in October and November 2002 at water temperatures of $6-16^{circ}C$ and salinities of 28.8-33.5 PSU. The highest concentrations of P. calliantha and P. fraudulenta were about $2{ imes}10^5;cells;L^{-1}$ and $1.5{ imes}10^5;cells;L^{-1}$, respectively. P. fraudulenta was found for the first time in the Russian waters of the East/Japan Sea. Morphological descriptions of these species based on observation with light and electron microscopy and information on their ecology are presented. Data on the geographical distribution of these species are supplemented.