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The fluorescence and nanozymatic nature of quantum dots (QDs) in a single entity provide an excellent opportunity for the development of sensitive fluorescence and colorimetric biosensing and bioimaging approaches. Herein, the hydrothermal synthesis method of fluorescent graphdiyne quantum dots (GDY QDs) from graphdiyne sheets is presented. This research reports, for the first time, the nanozymatic activity of GDY QDs besides their conventional fluorescent nature, which catalyzes the oxidation of H 2 O 2 through the peroxidase biomimetic nature and enables detection of H 2 O 2 and dopamine. The peaks of the ultraviolet−visible (UV−vis) spectrum and the fluorescence emission of GDY QDs are located at 395 and 450 nm, respectively. The X-ray photoelectron spectroscopic (XPS) results reveal that GDY and GDY QDs have similar carbon skeletons. Moreover, the intensity of C−O and C�O peaks in GDY QDs is stronger than that of GDY, suggesting the successful surface oxidation of GDY, which is crucial for hydrophilicity and catalytic activity. Kinetic analysis reveals that as-synthesized GDY QDs exhibit Michaelis−Menten kinetic behavior. The terephthalic acid and DPPH test confirms the hydroxyl radical formation and scavenging nature of GDY QDs, playing a significant role in enhancing the nanozymatic activity. The biomimetic nature of GDY QDs is applied for H 2 O 2 and dopamine detection, and limit of detection (LOD) values of 0.13 and 8.65 μM are obtained for H 2 O 2 and dopamine, respectively. The findings of this study will open a door to the development of carbon-based nanocrystals with an enzyme-mimicking nature that can lead to the development of analytical approaches, in particular, colorimetric nanobiosensors.