Herein, a novel "turn-on" fluorescent sensor was designed based on nitrogen-doped carbon dots (N-CDs) for the highly sensitive determination of morin. The N-CDs with orange fluorescent emission were prepared using neutral red and poly(ethyleneimine) as main sources via a hydrothermal approach. Interestingly, an enhanced fluorescence of N-CDs could be observed with the introduction of morin, which was attributed to the aggregation-induced emission-enhancement (AIEE) mechanism. The N-CDs presented a high sensitivity of fluorescence response to morin in the concentration range of 0.033-12.83 μM with a satisfactory detection limit of 29 nM. This method was also utilized for the quantitative determination of morin in human urine and serum samples with recoveries of 97.60%-103.90%. Moreover, the fluorescent hydrogel was further prepared by incorporating N-CDs into agarose and integrated with a smartphone-assisted platform, enabling semi-quantitative visual morin detection. Notably, this fluorescent sensor could also be applied for intracellular morin imaging due to its excellent hypotoxicity and biocompatibility, demonstrating that the proposed methodology holds great promise for biosensing applications.