The Hollywood star, 46, was pictured at the conference surrounded by an entourage and wearing a blue suit with a colourful lapel pin.
The actor, who is a United Nations representative on climate change, visited Kew Science's Carbon Garden space, where scientists will highlight the role plants can play in tackling climate change.
A spokeswoman for Kew Science, the research arm of Royal Botanic Gardens in Kew, said DiCaprio “seemed to enjoy seeing the wonderful display of plants and messages about nature-based solutions to climate change that the Kew’s display has on show”.
While DiCaprio was spotted at the summit, climate activists protested outside the Cop26 conference, ITV News Scotland Correspondent Peter Smith reports
DiCaprio has worked on documentaries about animal poaching and the environment, and was given his UN role in 2014.
He describes himself as an actor and environmentalist on Instagram.
His biography was updated with the hashtag #COP26 ahead of the event. He also added a link to the UN's webpage on climate change.
He was an executive producer on The Ivory Game, a 2016 documentary that examined the ivory trade.
Oscar-winning director Fisher Stevens also filmed DiCaprio as he travelled around the world to see the effects of global warming for the 2016 documentary Before The Flood.
Listen to Unscripted