Three men have appeared in court charged with producing cannabis after police executed a warrant on Friday in Llandysul.
Officers searched the former school on Heol Llyn y Fran on Friday, 15 November.
A large cannabis grow was located with 737 cannabis plants recovered.
Armeld Troski (29), Njazi Gjana (27) and Ervin Gjana (24) have all been charged with producing a controlled drug (class B) and have all been remanded in custody to appear at Haverfordwest Magistrates Court.
Police added on Monday, 18 November that officers remain at the scene whilst items are removed and further enquiries are carried out.
A spokesperson for Dyfed-Powys Police said: "Local officers would like to thank the community for their support and will continue to be present in the community whilst the building is secured.
"We are committed to making our force area hostile to those who produce and deal drugs.
“The local community can help us by continuing to report any signs of criminal activity – the easiest way to do this is on our website. Any bit of information, no matter how small it may seem, could help make a big difference."
Earlier this month, officers discovered more than 400 cannabis plants growing in a former supermarket in Newcastle Emlyn, a few doors down from the town’s police station.
And in July, a cannabis growing operation said to be worth £2 million was discovered in another former school in Llandysul, with around 1,500 plants seized.
A fire broke out at that school two weeks later.
If you’re concerned about drug-related crime in your area or think someone may be a victim of drug exploitation, please report it, either online at: , by emailing , or by calling 101.Alternatively, contact the independent charity Crimestoppers anonymously by calling 0800 555111, or visiting crimestoppers-uk.org.”