Objective To explore the changes of dopamine D2 receptor in dopamine pathway in insomnia patients and discuss its clinical significance. Methods From January 2016 to December 2016, 15 patients with insomnia (1 male, 14 females, age: (44.3±8.6) years) and 15 gender-/age- matched-healthy volunteers (control group; 3 males, 12 females, age: (40.5±9.0) years) were included to undergo resting brain 11C-Raclopride PET/CT imaging. The D2 receptor binding potential (BPND) of the dopamine pathway was calculated by molecular imaging and kinetic analysis toolbox (MIAKAT) software. The BPND, Hamilton depression scale (HAMD), transient and graphics memory scale results were compared with two-sample t test and Mann-Whitney u test between the two groups. Pearson correlation analysis was used to evaluate the correlation between BPND (nucleus accumbens, caudate nucleus, putamen) and Pittsburgh sleep quality index (PSQI), HAMD, course of disease, transient memory and graphical memory scale scores in the patient group. Results The BPND in bilateral putamen, nucleus accumbens and left caudate nucleus of patients was lower than that of controls(left putamen: z=-2.717, right putamen: z=-2.883, both P 0.05). The scores of HAMD in the patient group were higher than those in control group (t=10.273, P<0.01), while the scores of instantaneous memory (t=-4.888, P<0.01) and graphical memory scale (t=-2.624, P<0.05) were lower. There were significant negative correlations between the BPND of bilateral nucleus accumbens, caudate nucleus and putamen and the course of insomnia in the patient group (r range: -0.761 to -0.682, all P<0.01). Conclusion Patients with insomnia have abnormal neurotransmitter system of dopamine D2 and it may play a role in the pathogenesis of insomnia. Key words: Sleep initiation and maintenance disorders; Receptors, dopamine; Raclopride; Carbon radioisotopes; Positron-emission tomography; Tomography, X-ray computed; Magnetic resonance imaging