The Qizilsu (Tajik: Қизилсу) or Kyzylsu (‹See Tfd›Russian: Кызылсу) is a river that rises on the southern slopes of the Vakhsh Range in the north-east of Tajikistan's Khatlon Region and runs south-west until joining the Panj on the border with Afghanistan. The river is 230 kilometres (140 mi) long and has a basin area of 8,630 square kilometres (3,330 sq mi). It merges with the Yakhsu (Akhshu) as a major left tributary south of the town of Kulob. It irrigates the cotton-growing Qizilsu Valley between Kulob and Panj in the south-east of Khatlon Province. It is not the Kyzyl-Suu River that rises in Kyrgyzstan and flows through Tajikistan as Surkhob, then Vakhsh, following a course north-west of Qizilsu.

• "The Kyzylsu River and Mountains of Southern Tajikistan". Chelys. 30 November 2009. Retrieved 1 February 2019.