But Mr Trump said maximum sanctions and pressure on North Korea would continue ahead of proposed talks in May.
He added that denuclearisation of the Korean peninsula was now a possibility.
The comments follow Mr Kim's meeting with China's President Xi Jinping, in his first known foreign trip since taking office in 2011.
Mr Kim and his wife were greeted with a banquet and a guard of honour, with the North Korean leader reportedly saying he was committed to denuclearisation. China is North Korea's main economic ally.
On Wednesday, Mr Trump welcomed news of progress following the talks between the two leaders in Beijing after days of speculation.
"Now there is a good chance that Kim Jong-un will do what is right for his people and for humanity," Mr Trump posted, adding in the next tweet that Mr Kim also "looks forward to his meeting with me".