Officers executed warrants at addresses in Leyland, Liverpool and Croston on Wednesday (May 18).
Suspected drugs – believed to be heroin and cocaine – as well as mobile phones, cash and vehicles were seized by police.
Six people – five men and one woman – were subsequently arrested on suspicion of supplying a controlled drug
They were later released under investigation pending further enquiries.
Det Chief Insp Zoe Russo, of Preston Police, said: “We believe the individuals involved have brought Class A drugs into Lancashire, targeting the most vulnerable.
“We hope by doing this activity, not only will we disrupt and deal with the organised crime group, we can warn and educate young people about the consequences of such criminality.”
The raids were conducted as part of Operation Quarry – a major investigation into Class A drugs being brought into the county.
Operation Quarry was initially launched following the suspected distribution of drugs in the Leyland area.
"The widespread sale, distribution and use of Class A drugs leads to incidents of violence, threats and intimidation, exploitation, as well as family and community tension,” Det Chief Insp Russo added.
“Our operation has been in part supported by local people providing us with information.
“They are a vital source of intelligence and I would encourage them to keep assisting to help with our investigations.”
Anyone with information about drug dealing in their area can call 101 or contact Crimestoppers anonymously on 0800 555 111.