Leicester lost to Hull on penalties in the Capital One Cup on Tuesday night, but Ranieri was still pleased with the way Chilwell acquitted himself.
The youngster was making his full debut in the match, and Ranieri was delighted with the display that he put in.
"I'm very glad for the performance from Ben Chilwell because he played like a mature player," Ranieri said.
Chilwell is considered to be one of the Foxes' brightest prospects, and the 18-year-old will be hoping to stay around the first-team for the rest of the season now.
The defender has stood out at development level, and he certainly didn't seem overawed by the biggest occasion in his career to date at the KC Stadium.
Chilwell performed admirably against Championship high-flyers Hull, and he was very close to celebrating victory on his first start.
Leicester had taken the lead through Riyad Mahrez, but Abel Hernandez struck back for Hull and, ultimately, the Tigers won the match on penalties to reach the quarter finals of the competition.