Prisoner Jitendra alias Jeetu (27) shot another inmate Arjun (35) around 9.30 AM, apparently with a country-made weapon, Indore Superintendent of Police O P Tripathi said.
Arjun was immediately rushed to Maharaja Yeshwantrao Hospital where doctors declared him dead, he said.
Both Jitendra and Arjun were undertrials in separate murder cases, he said.
A probe has been launched into the incident and the prison administration is trying to find out how the prisoner managed to get the weapon inside the jail premises, the SP added.