Nicola Sturgeon said it was "democratically unacceptable" that Scotland faced the prospect of being taken out of the EU against its will.
She said the Scottish government would begin preparing legislation to enable another independence vote.
Scotland voted in favour of the UK staying in the EU by 62% to 38%.
The UK as a whole has voted to leave, by a margin of 52% to 48%, prompting UK Prime Minister David Cameron to announce he would stand down by October.
Read the full article: Nicola Sturgeon says second Scottish independence vote 'highly likely'