Melanoma, the skin cancer with the highest mortality rate, can be diagnosed at the early stage by detecting unique biomarkers. Over-expressed tyrosinase has been confirmed by dozens of clinical studies as an independent factor to evaluate the malignancy of melanoma. Using Enteromorpha Prolifera as the raw material, herein we develop a novel fluorescent probe, ECDY, which can sensitively detect the tyrosinase activity in different types of cells. More importantly, melanoma cells can be specifically distinguished through cell lysate measurements as well as the whole-cell imaging technique. Mechanically, the tyrosine groups on the surface of ECDY can be specifically recognized by tyrosinase and further converted into dopaquinone, which consequently causes the intramolecular fluorescence quenching of the probe through photoinduced electron transfer (PET). Tyrosinase can be detected within 20 min in the solution, and the detection limit is as low as 0.067 U mL−1. For the in vitro demonstration, we evaluate the fluorescence decay of ECDY in response to the intracellular tyrosinase activity within the lysate of various cell lines, including non-cancerous, non-melanoma cancerous, and mouse melanoma ones. The experimental results verify that ECDY can accurately measure the apparent tyrosinase activity in different cell lines and detect melanoma cell lysate specifically. The confocal fluorescence imaging experiments further demonstrate that ECDY can distinguish melanoma cells from others significantly. We believe that ECDY provides a new strategy for the efficient detection of tyrosinase and melanoma cells, and is expected to apply as a clinical diagnosis platform. Display omitted •A fluorescent tyrosinase probe was synthesized using Enteromorpha Prolifera as the raw material.•Tyrosinase in solution at 0.067 U mL−1 can be detected with high selectivity.•The apparent activity of tyrosinase in different cell lines can be evaluated through cell lysate measurement.•The probe can be effectively internalized into various cells and distinguish living melanoma cells from others.