Dr Avraham Katznelson (Hebrew: אברהם קצנלסון, also known as Avraham Nissan, born 1888, died 18 May 1956) was a Zionist political figure in Mandate Palestine and a signatory of the Israeli declaration of independence.
Katznelson was born in 1888 in Babruysk in the Russian Empire, now in Belarus. A doctor and resident of Jerusalem, Katznelson was a member of the central committees of both Mapai and Hashomer Hatzair, representing the former in the Vaad Leumi and Moetzet HaAm, and also serving as director of the health department of the Zionist Executive. As such, in 1948 he was amongst the signatories of Israel's declaration of independence, and was immediately co-opted into the Provisional State Council. He was also involved in the foundation of the radio station Kol Yisrael, which began broadcasting on the day independence was declared.
After independence he was appointed as an envoy to Scandinavia and later took a Hebrew surname, Nissan.
His sister Rachel Katznelson-Shazar was the wife of President Zalman Shazar, whilst he was the uncle of Shmuel Tamir.