Tuna fisheries have become the most important contributor to the coastal central provinces of Vietnam since it was introduced in early 1990s. However, developing effective management guidelines for yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna, the main target species for longline and handline fisheries, is difficult because there is no information on its growth characteristics. In particular, length-length, length–weight, and weight-weight relationships, the important components of fisheries production models, do not exist for those species. This study first provided those relationship equations and represented an improvement in the knowledge of these species in its distribution range with maximum sizes updated.