Paul Willoughby Ramell, of Hill View Road, Garstang was described as a predatory individual by police officers who helped to bring him to justice.
The 66-year-old was charged after his victims, who cannot be identified for legal reasons, came forward to report the historic sexual abuse, which happened in the Preesall area in the 1980s.
One of the youngsters was raped by Ramell as she sat on a beanbag.
Another victim was warned: “Don’t tell your mum” as he subjected her to sexual abuse.
Both girls were touched inappropriately and forced into committing acts with Ramell over a period of several years.
During a hearing before Preston Crown Court Ramell pleaded guilty to rape and several indecent assaults Judge Simon Newell jailed him for 20 years.
He was also given a one year extended licence period - which means he will be supervised in the community - and will be made to sign on the sex offender’s register for life.
He will be barred from working with young people and vulnerable adults on his eventual release from prison.
Speaking after the case, Det Con Steve Jenkinson, of Lancashire Police, said: “Paul Ramell is a predatory individual who subjected his victims to a number of horrific sex assaults and rapes over several years.
“I am pleased he has been brought to justice and he will now be in prison for a significant period of time.
He paid tribute to the women, adding: “The victims in this case have shown a tremendous amount of courage throughout this investigation and I hope the sentence will allow both women to begin to put this ordeal behind them and move forward with their lives.
“If anyone has been the victim of a sexual offence, I would urge them to come forward and report it to us in the knowledge that we take all reports seriously and ensure that victims are treated sensitively and professionally at all times.”