John Somerville, 57, plied the boys with alcohol, started games which ended with the boys having to take their clothes off as forfeits and sexually abused them.
The three victims, aged between 13 and 14, were groomed by the scout leader at his Glenrothes group.
Somerville preyed on the youngsters after taking them on camping trips across Scotland in the 1990s.
Two of his victims were in court to see Somerville sent to prison.
He had avoided jail after being convicted of similar offences in 2006 and had gone on to run a gardening business.
Somerville, of Greenwell Park, Glenrothes, was sentenced this week at Dunfermline Sheriff Court having previously admitted a catalogue of offending against the boys.
On various occasions between September 24, 1996, and September 23, 1998, at Hatton Green and Jubilee Centre, Glenrothes, within a vehicle travelling to various locations within Fife and Glasgow and at various camping locations in Scotland, he indecently assaulted a boy then aged 14 years. This included removing his clothing, touching and kissing his private parts and inducing his to perform a sexual act.
Somerville also admitted that on various occasions between June 29, 1996, and June 25, 1997, at Hatton Green, Glenrothes and various camping locations in Scotland, he used lewd, indecent and libidinous practices towards another boy then aged 13.
He provided him with alcohol and incited him to play indecent games which resulted in the boy having to remove his clothing. He incited the boy to kiss other scouts on the mouth and body and induced him to be present during sexual activity between Somerville and other scouts. He also induced the boy to lick his (Somerville’s) naked genital area and induced him to lick the genitals of other scouts.
He instructed the boy to remove his clothing and perform naked press-ups.
Somerville also admitted that on an occasion between December 25, 1998, and February 28, 1999, at Hatton Green, Glenrothes, he indecently assaulted a third boy then aged 14 by inducing him to pull his trousers down, and then licked his genital area.
Sheriff William Gilchrist said it was not clear from the social work report whether Somerville was indeed remorseful.
The sheriff said his actions were “a serious breach of trust, involved a degree of planning and targeted vulnerable children.”
He jailed Somerville for 45 months backdated to March 9 when he was remanded in custody.
Somerville will also be subject to a 12-month supervised release order and was put on the sex offenders register indefinitely.
In November 2006, at the same court, Somerville was found guilty by a jury of offering money to two boys, aged 12 and 13, to take part in sexually intimate games with him between 2001 and 2002.
One of the offences took place during an overseas trip to a scout camp in the USA.
In the 2006 case, Somerville was sentenced to 300 hours of community service.