We tested temperature-size and resource-size relationship in determining phytoplankton normalized biomass size spectral (NBSS) slopes in the Kuroshio east of Taiwan. We used phytoplankton total biomass as a proxy for resource supply instead of inorganic nutrients because inorganic nutrients cannot be a reliable proxy for resource supply in oligotrophic oceans. We found a positive relationship between phytoplankton NBSS slopes and total biomass, generally supporting the resource-size relationship. The only exception occurred in spring, during which the NBSS slopes deviated downward from the regression. In spring, we observed that small cells were dominant as nutrient pulses in the Kuroshio region, which is contrast to expectation from the resource-size relationship. This discrepancy can be explained by the none-steady state theory, where in the initial stage of nutrient enrichments in oligotrophic regions in spring, that small cells with a high surface-area-to-volume ratio uptake nutrients faster than the larger ones.