Hamazasp "Hamo" Ohanjanyan (Akhalkalak, 1873 – Cairo, 31 July 1947) was an Armenian doctor, revolutionary, and politician.

He served as the third Prime Minister of the First Republic of Armenia from May 5 to November 23, 1920.

Hamo (Mher) Ohanjanyan studied in Akhalkalak, his birthplace. He later moved to Tbilisi and graduated from the Tbilisi Russian Lyceum. In 1892 he continued his studies in Moscow University and entered the School of Medicine. However, he left school early in order to join the Armenian revolutionary movement. He traveled to Lausanne, where he met Kristapor Mikayelian, one of the founding members of the Armenian Revolutionary Federation.

After the Russian revolution of March 1917, he was elected a member of the Russian Assembly and then became a member of the Transcaucasian Seim in 1918.

In early 1920 he went to Yerevan and took up the position of Foreign Affairs Minister of the newly founded First Republic of Armenia in the cabinet of Prime Minister Alexander Khatisian. After the resignation of Khatisian's government following the Bolshevik uprising of May 1920, Hamo Ohanjanian became Prime Minister until November 23, 1920, when his cabinet resigned amid the crisis generated by the Armenian-Turkish war.