In a tweet criticising his Democratic rival Hillary Clinton, Trump wrote, "Hillary Clinton should not be given national security briefings in that she is a lose cannon with extraordinarily bad judgement and insticts."
Trump's tweet echoed a statement made by Clinton in May, when she called him an "unqualified loose cannon".
Twitter users were quick to point out the three spelling mistakes in his short tweet -- 'lose' instead of 'loose', 'insticts' instead of 'instincts', and 'judgement' instead of the correct US spelling of the word 'judgment'.
"Make America Spell Again @realDonaldTrump," tweeted another user.
This is not the first time the Republican presidential nominee has misspelled words or made typos on the social network.
"Every poll said I won the debate last night. Great honer!" he wrote in February, in a tweet that has since been deleted after people pointed out the correct spelling was 'honor'.