The suspects--Deepak Chandra, Raj Kumar, Arif Khan and Prakash-- were arrested yesterday, they said.
The arrests were made following a tip-off that some men had set up the online casino in Kotla Mubarakpur, said Deputy Commissioner of Police (South) Ishwar Singh.
The police also seized Rs 35,800 in cash, computers and other materials from the suspects.
It was found that Chandra had been involved in running the casino from a building, they said.
During the interrogation, the suspects revealed that the mastermind of the racket was one Neetu, who has earlier been linked to another online casino syndicate, Singh said.
Chandra used to submit all transaction details to Neetu, who is currently on the run, he said.
It is also suspected that the account may be linked to other similar accounts engaged in money laundering, police added.