Abstract: To facilitate the accurate and rapid detection of mercury (II) ions (Hg²⁺) in drinking water, an innovative "turn-on" fluorescent aptasensor was developed. This sensor was able to quantitatively detect Hg²⁺ through the mechanism of Fluorescence resonance energy transfer (FRET) between a Hg²⁺-specified aptamer modified with boron-doped carbon quantum dots (BCQDs-Apt_Hg) and its complementary strand labeled with a Black hole quencher 1 (CS_Hg-BHQ1). The fluorescence characteristics of the BCQDs were thoroughly characterized, and the BCQDs-Apt_Hg probe was synthesized by conjugating the BCQDs with an amino-modified aptamer. The fluorescent aptasensor was subsequently constructed by forming a complex probe between BCQDs-Apt_Hg and CS_Hg-BHQ1. Additionally, the detection conditions, analytical performance, and practical applicability of the constructed aptasensor were systematically investigated. Characterization results demonstrated that the BCQDs exhibited excellent photostability and were successfully conjugated with the aptamer. Optimal experimental conditions were established by optimizing several parameters, including an incubation time of 10 minutes for both BCQDs-Apt_Hg and CS_Hg-BHQ1, concentrations of 347 nmol/L for BCQDs-Apt_Hg and 600 nmol/L for CS_Hg-BHQ1, and the use of HEPES buffer at pH 7.8. Under these optimal conditions, the developed sensor achieved a limit of detection (LOD) of 0.81 nmol/L with a rapid assay time of only 20 minutes. Moreover, it demonstrated high selectivity and specificity against various interfering ions. When applied to the analysis of real water samples, the sensor yielded excellent recoveries ranging from 93.40% to 115.33%, satisfying the requirements for testing against the national safety limit for Hg²⁺ in drinking water. This work presents a sensitive, efficient, and cost-effective strategy for Hg²⁺ detection in water samples, contributing to the development of novel rapid-detecting methods for Hg²⁺ contamination.