As an essential micronutrient for all organisms, Fe has been recognized as a factor to regulate climate change by influencing primary production in the ocean. It was also found that iron may limit the primary productivity in some oligotrophic region by limiting nitrogen-fixing organisms. In order to better understand the relationship between Fe and N-fixing activities, we have occupied 26 stations in the southwest Pacific between 14-30 degS and 147-190 degE (March-April 2007) collecting data for hydrography (T,S), nutrients (P, N) and samples for Fe from the euphotic zone (17 stations). Surface maxima with subsequent minima in Fe was observed in southwest Pacific euphotic zone, the Fe minimum in subsurface waters is alway associated with the chlorophyll maximum. Southwest Pacific surface waters are strongly N-limiting, with comparison of nutrients data (N, P, Si) in the southwest Pacific euphotic zone, the Fe concentrations with an average value of 0.27 nmol/kg observed in surface waters supported phytoplankton growth that were iron-stressed. At the depth of 70-100 m in the euphotic zone where Fe concentrations are near or less than 0.12 nmol/kg, Fe concentrations turn to iron-limitation. At several stations, N-fixing blooms in the southwest Pacific coincide with higher Fe in the euphotic zone. Although it was suspected that high Fe would simulate or maintain diazotrophs bloom, this is the first field observation of this relationship.