Objective. To detect blood plasma coagulability in children with mental diseases using a thrombodynamics test. Material and methods. The study included two groups of children. Group 1 included 11 patients with infantile psychosis in autism (F84.02) (4 girls and 7 boys). Group 2 included 8 patients with childhood schizophrenia (F20.8xx3) (4 girls and 14 boys). A test was performed with T-2 Thrombodynamics analyzer (LLC Hemacore, Moscow, Russia). Results. Thrombodynamic parameters, such as initial, steady-state velocity and spontaneous clots adjusted velocity (Vi, Vst and V, μm/min, respectively) and clot size at 30 minute of thrombodynamics test (CS μm) were significantly increased in the total group of patients (n=29). The time of appearance of spontaneous clots (Tsp), the time of clot lag time (Tlag) and clot density (D) did not differ significantly from the normal values (p=0.98; p=0.27 and p=0.21, respectively). In the autism group (n=11), Vi, Vst and V were significantly higher than normal values, while CS, Tsp, Tlag and D did not differ from norm. In the schizophrenia group (n=18) V, Vst and CS, and Vi were significantly increased. Tsp, Tlag and D did not differ from normal values. Differences between the parameters of thrombodynamics in 1 and 2 groups were not statistical significant. Conclusion. It was shown for the first time that clotting (hypercoagulability) of the blood plasma in patients with autism and childhood schizophrenia was increased. This can cause thrombosis in small vessels of the brain. Early spontaneous clots appear in many patients that indicating the presence of systemic inflammation, possibly associated with an exacerbation of neuroinflammation. The thrombodynamics test allows detection of predisposition to hypercoagulability in the early stages when other methods are not sensitive enough.