The effects of different nutrient supply on the maximal quantum yield of photosystem Ⅱ (Fv/Fm) to Scrippsiella trochoidea in nitrate\|starved and phosphorus\|starved cultures were monitored in order to find weather it could be used to determine N and P limitation of S. trochoidea. The results showed that Chl a contents of N\|starvation culture increased at first and then declined significantly after nitrate was exhausted, while Chl a contents of P\|starvation culture increased initially and then declined slowly after phosphate was exhausted. Fv/Fm remained stable throughout the N\| and P\|starved incubation. When sufficient nitrogen and phosphorus were resupplied to N\| and P\|starvation cultures of S. trochoidea respectively, Chl a contents increased rapidly in 48 hours in N\|starvation culture while it showed no obvious change in P\|starvation culture. There was no measurable increase of Fv/Fm to nutrient addition in both of the two cultures. Our study demonstrates that Fv/Fm cannot be used for the detection of nitrogen limitation and phosphorus limitation of S. trochoidea. This method has limitations on the detection of nutrient stress for phytoplankton.