We describe a Chinese family with severe autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE) and psychiatric problems in whom whole-exome family trio sequencing identified a heterozygous mutation in the potassium channel subfamily T, member 1 (KCNT1), a sodium-gated potassium channel gene, which was a novel missense mutation c.2153A>T (p. Asp718Val). The typical characteristics of the three patients in the family were refractory epilepsy, acquired cognitive impairment, and psychiatric problems, which include hallucinations and suicidal thoughts and behaviors. The age at onset was found to be earlier in son and daughter of the proband than that of the proband, as proven by the proband's history of an epileptic seizure at the age of 16 years and her son's and daughter's history of seizures at the age of 8 years. Magnetic resonance imaging findings were negative for any abnormalities. Because of psychiatric symptoms, these three patients were administered risperidone at different times during their illness. The protestor's son had tried fenofibrate treatment, but clinical remission was unclear. In summary, our findings broadened the mutation database in relation to KCNT1 and implicated the sodium-gated potassium channel complex in ADNFLE, more broadly, in the pathogenesis of focal epilepsies.