Junko Saito (斉藤淳子, Saitō Jun'ko) (née Nakajima (中島淳子, Nakajima Jun'ko, born 2 May 1952), more commonly known by her stage name Mari Natsuki (夏木マリ, Natsuki Mari), is a Japanese singer, dancer and actress. Born in Tokyo, she started work as a singer from a young age. In 2007, Natsuki announced her engagement to percussionist Nobu Saitō, with their marriage taking place in Spring 2008.

Natsuki has participated in musical theatre, including Madame Thenardier in Les Miserables, Golde in Fiddler on the Roof and that of Yukio Ninagawa. She provided the voice of Yubaba in Spirited Away, played the young witch's mother in the Japanese TV remake of Bewitched and has twice been nominated for a Japanese Academy Award. Natsuki played the character Big Mama in the Japanese version of Metal Gear Solid 4: Guns of the Patriots and has also acted in television dramas, such as the 2005 series Nobuta o Produce, playing the Vice Principal, Katharine.

In 2024, Natsuki reprised her famous roles of Yubaba/Zeniba for the stage production of Spirited Away, performing in Japan and London.