Local police suspect that older children stole copper sulphate from a school laboratory and fed it to younger children in a Potteresque initiation ceremony.
The 23 children taken to hospital are out of danger, but the police have launched a criminal investigation, accusing the school of not storing its chemicals properly.
Harry Potter and the Goblet of Fire, the fourth book in the bestselling series by JK Rowling, went on sale in Moscow on Saturday, feeding the growing Potter mania.
School hazard
Investigator Sergey Krechkov said children seemed to have "unlimited access" to chemicals in School No. 182.
The school denied the allegation.
A reporter from Moscow's Komsomolskaya Pravda newspaper who went to the school, said children told him they had been inventing potions and ceremonies.
"He said there would be some initiation, so we came to the classroom and tried it," Sergey Ivanov, one of the pupils, told Russian NTV television.
Other students told NTV they would try a "magic potion" if it were offered to them. 
The fourth Harry Potter book has just come out in Moscow