Four people were arrested in connection with the bust, which include 420 kilograms (926 lb) of crystal methamphetamine as well as heroin at a home in Nakhon Pathom province, north of the capital Bangkok.
"This is one of the largest drug storage facilities in the middle of Thailand, in a community area," Justice Minister Tawee Sodsong told reporters.
Incoming police chief Police General Torsak Sukvimol said the overall street value of the bust was 300 million baht, adding that the drugs were produced in a neighboring country.
Trafficking of synthetic drugs in East and Southeast Asia is surging, the United Nations said in a report earlier this year, with high volumes of methamphetamine still being produced from the Golden Triangle region where the borders of Myanmar, Thailand and Laos meet.
The region has a long history of illicit drug production and has recently served as a massive production center for amphetamine-type stimulants, especially methamphetamine, used by Asian crime syndicates with distribution networks reaching as far as Japan and New Zealand.