In the present study, a facile fluorescence turn-on approach for the detection of alkaline phosphatase (ALP) activity has been developed. L-ascorbic acid-2-phosphate (AAP), a substrate of ALP, could be hydrolyzed by ALP to give L-ascorbic acid. L-ascorbic acid then reduced resazurin to resorufin, which resulted in a turn-on fluorescence signal. The fluorescence intensity increase could be directly related to the amount of ALP added to the assay solution. The assay is very sensitive, as 0.12 mU mL⁻¹ ALP could be clearly detected. Sodium orthovanadate (Na₃VO₄), a well-known ALP inhibitor, was tested, and a clear inhibition effect was observed. The results suggest that our method could be used for ALP activity sensing related various biochemical applications and for the screening of ALP inhibitors.