Acting on a tip-off, the immigration police obtained a warrant for searching the eighth and ninth floors of a hotel in Ngam Wong Wan.
Apart from the 26 alleged gamblers, the immigration police arrested 23 Thai staff.
Police seized six baccara desks, six slot machines, a game machine, and over 100 card sets as well as 3.5 million in cash and chips representing tens of millions of baht.
The immigration police said they had received a tip-off that the gambling den had been operating for a long time.
The suspects and evidence were handed over to the Ratanathibet Police Station, which is in charge of the area, for legal actions.
Since local police did not take part in the raid, the top five officers are expected to be suspended from duty and face a disciplinary probe.