The study aimed to investigate the expression and significance of the plasma let-7 family in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis. Blood samples from 5 anti-NMDAR encephalitis patients and 5 negative controls were collected for microarray analysis. Blood samples from10 anti-NMDAR encephalitis patients, 10 anti-NMDAR encephalitis patients whose physical conditions have improved after 3 months of immunotherapy, 20 virus (meningitis) encephalitis patients, 20 tuberculosis (meningitis) encephalitis patients, 10 purulent (meningitis) encephalitis patients, 20 cerebral cysticercosis patients, 20 ischemic stroke patients, 20 intracerebral hemorrhage patients, 15 neuromyelitis optica patients, 15 multiple sclerosis patients, 15 moyamoya disease patients, and 20 negative controls were collected for real-time quantitative PCR (qRT-PCR) analysis. The expression levels of let-7a, let-7b, let-7d, and let-7f were significantly down-regulated in anti-NMDAR encephalitis compared with the negative controls (NC). The expression levels of let-7a, let-7d, and let-7f were significantly down-regulated in other nervous system diseases compared with the NC group while the expression level of let-7b was statistically insignificant in other nervous system diseases compared with the NC group. In addition, there was no significant dysregulation of let-7b in the anti-NMDAR encephalitis treatment group compared with the NC. Let-7b may be a potential diagnostic marker and an indicator that reflected the molecular mechanism of anti-NMDAR encephalitis.