A photoluminescent probe for Mn²⁺ detection was constructed using photoluminescent carbon quantum dots (CQDs) obtained from the traditional Chinese medicinal material Magnolia officinalis as the carbon source via a one-step hydrothermal method. These CQDs exhibit excellent photoluminescence performance, including a maximum excitation wavelength of 285 nm, maximum emission wavelength of 425 nm, and a photoluminescent quantum yield of 28.4%. The Mn²⁺ photoluminescent probe shows exceptional selectivity, excellent anti-interference ability, and high sensitivity. Over the Mn²⁺ concentration range of 0.2?800 μmol/L, a linear correlation exists between (I₀-I)/I and Mn²⁺ concentration, with a correlation coefficient of 0.9996 and a low limit of detection at 52 nmol/L. Mn²⁺ in real water samples was detected by adding 5, 50, and 100 μmol/L Mn²⁺ to the samples. The relative standard deviations were 0.9%?2.9%, and the recoveries were 98.8%?101.5%. This novel CQDs photoluminescent probe has broad application prospects in the environmental analysis of Mn²⁺.