The Imperial Senate was the de jure legislative council of the First Galactic Empire. It was the successor to the Galactic Senate of theRepublic, which was reformed into an autocratic regime when thenSupreme Chancellor Sheev Palpatine declared himself Emperor.
The Imperial Senate was disbanded after the capture of Princess Leia Organa of Alderaan nineteen years after the formation of the Empire. With Leia being a senator who supported the growing Rebellionagainst Palpatine's absolute rule, the Emperor used the incident to cast doubt unto the loyalty of the assembly. As such, the Senate's former prerogatives were handed down to the regional governors and the military.
(source wookiepedia)