Synthetic cannabinoids (SCs) are a series of artificial chemical substances with pharmacological properties similar to those of natural cannabinoids and their abuse poses a great risk to social security and human health. However, the highly sensitive detection of low concentrations of SCs in human serum remains a great challenge. In this work, we developed a highly sensitive, rapid and highly selective method for the detection of SCs in human serum. Magnetic molecularly imprinted polymer (MIP) nanocomposites were prepared through self-polymerization of dopamine and template molecules on the surfaces of magnetic beads. 9H-Carbazole-9-hexanol (9CH) was used as a template molecule because of its long chain structure shared with six synthetic cannabinoids and its ability to provide specific recognition sites. With these magnetic MIP nanoparticles, six SCs could be rapidly and effectively extracted from human blood. The concentrations of six SCs could be accurately determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. The limits of detection were in the range of 0.1-0.3 ng mL-1. The proposed method is characterized by high sensitivity and selectivity, and has great potential for application in the analysis of practical samples.