Objective To investigate the changes of amine β hydroxylase activity （DβH） in patients with schizophrenia and clinical ultra-high risk individuals and its relationship with psychotic symptoms. Methods 61 schizophrenia patients admitted to Beijing Anding Hospital affiliated to Capital Medical University， 35 clinical ultra-high risk participants and 86 sex-matched healthy controls were included in this study， which is designed by the cross-sectional group research method. To analyze the effect of long-term administration of antipsychotics on DβH， 39 patients with chronic schizophrenia were also included. The Positive and Negative Syndrome Scale （PANSS） was used to evaluate the psychotic symptoms of the patients. The plasma DβH activity was detected by high performance liquid chromatography and electrochemistry in participants. The differences of plasma DβH activity and psychotic symptoms among first-episode schizophrenia patients， clinical ultra-high risk individuals， and the healthy controls were analyzed. Further comparison of the plasma DβH activity between first-episode untreated schizophrenia patients and chronic treated schizophrenia patients were carried out to analyze the impact of antipsychotics on plasma DβH activity. Results There was a statistically significant difference （F=6.591， P=0.002） in plasma DβH activities among first-episode schizophrenia patients ［（12.35±8.55）nmol/（ml·min）］， clinical ultra-high risk individuals ［（19.59± 13.95） nmol/（ml·min）］ and healthy controls ［（17.51±11.04） nmol/（ml·min）］. The plasma DβH activity in schizophrenia patients was significantly lower than those of healthy controls （P ＜ 0.05） and the clinical ultrahigh risk individuals （P ＜ 0.01）. However， there was no statistically significant difference in plasma DβH activities between clinical ultra-high risk individuals and healthy controls （P＞ 0.05）. No significant correlations were found between plasma DβH activity and course of disease， positive symptoms， negative symptoms， and general psychotic symptoms in schizophrenia patients （P ＞ 0.05）. Plasma DβH activity in the first-episode untreated patients was significantly lower than those in the first-episode treated patients （t=2.023， P=0.048） and the chronic treated patients ［（18.52±7.00） nmol/（ml·min）， F=7.053， P=0.010］. Conclusions Plasma DβH activity in first-episode untreated schizophrenia patients significantly decreased compared with that in the healthy controls. Short-term or long-term treatment of antipsychotics could increase plasma DβH activity in schizophrenia patients.