Effects of four novel atypical antipsychotic drugs (olanzapine, perospirone, quetiapine, and risperidone) on scalp-recorded multi-channel EEGs were compared with two conventional antipsychotic drugs (chlorpromazine and haloperidol) and placebo in 14 healthy male volunteers. All subjects went through seven sessions. In each session, EEGs were recorded before and 2, 4 and 6 hours after drug administration. Global Field Power (GFP) in delta frequency band (1.5-6 Hz) increased around the time of peak serum concentration of quetiapine and risperidone compared to baseline. The increase of GFP in delta activity after quetiapine was significantly prominent in comparison to two other atypical antipsychotic drugs, perospirone and olanzapine, as well as to typical antipsychotic drugs, chlorpromazine and haloperidol (p<0.05). The increase in GFP of delta after risperidone was more prominent in comparison to after haloperidol (p<0.05). The greater sedative effects after quetiapine and risperidone may reflect the high affinity to A1 and H1 receptor bindings of these drugs. According to Low Resolution Electromagnetic Tomography (LORETA), olanzapine increased the delta in the posterior region indicating a frontal shift of brain activity, suggesting that olanzapine may be useful against negative symptoms in schizophrenics.