The polling began at 7 AM and will continue till 5 PM.
No untoward incident was reported in the initial hours.
As many as 1,88,839 voters are eligible to excise their franchise.
Police have put in place elaborate security arrangements and five major check points have been set up at the entry points in the constituency.
Six contingents of central security forces have been deployed.
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Live webcasting and videography of polling process was also being done, district officials said.
The by-election was necessitated following the death of the sitting Congress MLA Patlolla Krishna Reddy, popularly known as Kishta Reddy.
Ruling TRS candidate Bhupal Reddy is pitted against his brother, TDP candidate Vijaypal Reddy, while Congress has fielded Sanjeev Reddy, son of the deceased MLA as its nominee.
The counting of votes will be held on February 16.