Rao was kidnapped by suspected militants of the National Democratic Front of Bodoland (NDFB) from a road construction site in Kokrajhar district.
"After reaching Kajalgaon he straightaway came to his company office and then police were informed about his release by some of the staff of Gayatri Construction," the official said.
It was not immediately known if his family or officials of the Gayatri Construction Company paid any ransom money to the NDFB to secure his release.
50-year-old, Rao hails from Gannavaram in the coastal Krishna district of Andhra Pradesh and was a diabetic requiring constant medication.
"What appears from the initial conversation with Rao was that he was treated well by the captors and his medical needs were taken care of during the past one month in captivity," the official added.