David Bell Bryson, who was born in Larkhall, South Lanarkshire, strangled Stanislav Mirchev to death in the village of Lagoshevtsi, in the north-west of the country, in January last year.
The 72-year-old had earlier told the court he killed the boy in a state of uncontrolled anger after the youngster tortured his dog, but later changed his plea to not guilty.
He was convicted of murder at Vidin Regional Court and was also ordered to pay 200,000 Bulgarian Levs (£84,000) in compensation to his victim's family.
Prosecutors had asked the court to impose a sentence of life without parole because of the cruelty of the murder, but this was rejected.
Bryson's defence counsel claimed the murder charge was only based on the pensioner's confession during the investigation.
After the trial, the boy's father, Veselin Mirchev, said he was not satisfied with the sentence, adding that he wished Bulgaria still had the death penalty.
Bryson confirmed he would appeal against the verdict and maintained his innocence.
Stanislav, who used to carry out chores for Bryson, disappeared on January 4, 2012.
A major search was launched to find the child a couple of days later.
His body was discovered in undergrowth on the outskirts of the north-western village on January 18 and two days later Bryson was detained as the main suspect.
Prosecutors claimed the murderer failed a lie-detector test before agreeing to plead guilty to the crime.
Bryson – who moved to Bulgaria two years before the murder after working in Germany as an aviation mechanic – claimed the boy had tortured his dog, and he killed him in a state of rage. He was expected to plead guilty and be given a more lenient sentence which could be served in Britain.
However, in September, he changed his plea to not guilty.
He told the court at that time: "I will not plead guilty. I have not seen the kid on that date and I have not killed him."
Forensic examinations of the boy revealed he had been involved in sexual activity before he died, but no charges of this nature were brought against Bryson, who still has family in Scotland.
Reports suggested Bryson paid the boy to do odd jobs around his home and took photos of him as he did so.
Villager Veselka Kostova said: "I only spoke to him a couple of times. He said he'd come to Bulgaria because it was cheaper and his pension would last longer than in Scotland.
"He told me he was divorced and had three children – daughters.
"He would sometimes hire local children to help him with repairs around the house, and he photographed them."
Following Bryson's arrest, chief investigator Vladislav Vlashev said he had shown "no remorse" for the killing.
The senior police officer said: "He displays little respect and even laughs about the boy's death. He seems to have no remorse and says the boy deserved to die for poisoning his dogs."
The prosecutor in the case intends to appeal and apply for Bryson to be given a life sentence without parole.