It followed criticism from Euan Blockley, who had expected to top one of the UKIP regional lists for Holyrood in May.
Mr Blockley has alleged that the process was "stitched up" by the party leadership to favour their friends.
He told BBC Scotland that he has left the party as a result.
At 18 years old, Mr Blockley would have been one of the youngest candidates standing in the election.
He said: "I've ripped up my party's membership card. The party has "stitched up" the party lists - and it goes all the way David Coburn - the NEC etc - giving list places to their cronies.
It was meant to be a democratic process, when the lists would be chosen by the party members - that's what we were promised."
Although he believes he would have been placed second on a regional list, he said he is horrified by the way UKIP in Scotland carried out the process.
Mr Blockley added: ""It's a country club - all the placements are being handed out to friends - at the expense of good candidates."
UKIP has insisted the selection of candidates was carried out properly.
Scottish leader David Coburn said: "The final pool of candidates and their position on any list is agreed by a ballot of the party's National Executive Committee.
"The NEC is elected by the party membership and is therefore democratically accountable to the party membership."
UKIP in Scotland has defended its procedures for selecting Scottish parliamentary candidates as being "democratically accountable".