RFE/RL's Kyrgyz Service says more than 10,000 people took part in the March 1 rally.
Protesters backed Osh Mayor Melis Myrzakhmatov and criticized President Almazbek Atambaev.
Adakhan Madumarov, leader of the Butun (United) Kyrgyzstan party, addresses the rally.
The opposition Ata-Jurt (Fatherland) party is strong in Osh.
Ata-Jurt party leader Kamchybek Tashiev also addressed the rally.