Continuous flow method was examined for the determination of phosphorus. The molybdophosphate formed between orthophosphate and molybdate in hydrochloric acid medium diminished the fluorescence of Rhodamine 6 G. Carrier solution (distilled water) and reagent solution were propelled by double plunger pump P₁ and P₂ (flow rate : 0.98 ml/min), and sample solution(160μl) was injected into the carrier stream. The two streams were mixed in 20 cm long Teflon tubing (1 mm i.d.), and the mixture was flowed through a flow cell(18μl), at which the fluoresence of Rhodamine 6 G was detected(λ_ex =350 nm, λ_em=580 nm). The reagent solution consists of 0.035 M molybdenum and 1 × 10^-5 M Rhodamine 6 G in 0.8 M hydrochloric acid. Co-existing ions generally existing in river and sea waters did not interfere the determination of phosphorus. The calibration curve was linear from 0 to 45 ppb of phosphorus. The method was applied to sea water. The sampling rate was 20 samples per hour.