The development of potential magnetic materials in metal-doped polycyclic aromatic hydrocarbons has been a research hotspot in recent years. Here we have successfully synthesized stable potassium-doped 2,3-dimethylnaphthalene samples. The combination of first-principles calculations and XRD results identifies that doping of potassium into 2,3-dimethylnaphthalene forms a monoclinic structure with a molar ratio of 1:2 between potassium and molecule. The red shifts in the Raman spectra indicate that potassium 4s electrons are transferred to the organic molecules. The magnetic measurements show that the doped materials exhibit a temperature-independent magnetization in the temperature region of 1.8–300 K, which is consistent with the Pauli paramagnetic behavior. This is distinct from the diamagnetism of pristine material. Compared to the previous focus on benzene ring structure, our study of aromatic hydrocarbon derivatives of benzene ring opens a new route for the development of this field.