ABSTRACT: The importance of the deep, cold-water hexacorals as cold-water bioherms and their contribution to marine carbonate production has been demonstrated elsewhere. However, no research has been carried out to examine the contribution of carbonate production by deep, cold-water octocorals (CWOC), even though this group comprises a major component of cold-water coral fauna in the NW Pacific. To assess the contribution of CWOC carbonate production on the Shiribeshi Seamount (43°34–36’N, 139°31–35’E), Sea of Japan, remotely operated vehicle (ROV) dive video archives and deposited specimens of Primnoa pacifica (Octocorallia, Primnoidae) were analysed. To estimate the carbonate weight per colony, the diameter of cross-sections of branches or stems and the carbonate weight per volume of specimens were measured. Colony volumes were then calculated from the video footage. The amount of carbonate standing stock (CSS) was calculated at each dive line by analysing the distribution of CWOC and specimen data. The average (±SD) weight percentage of sclerites per colony of P. pacifica was 37.93 ± 7.45%, with the range 25.47 to 49.19%. It was estimated that the total amount of CSS of coral would be over 0.65 t at all dive lines (22753 m²) at the seamount. Maximum CSS was 70.64 g m^–2 and maximum carbonate production was up to 3.61 ± 0.06 g m^–2 yr^–1. In comparison with the other CSS in non-tropical areas, our results show that CWOC may potentially contribute to carbonate production in cold-water environments.