She returns to power nearly eight months after she was forced to quit over corruption charges.
Jayalalithaa took the oath in the name of God in Tamil in a simple function held at the University of Madras Centenary Auditorium here. Twenty-eight other ministers also took oath in a brief ceremony.
The 67-year-old AIADMK supremo was administered oath of office and secrecy by Governor K Rosaiah.
Earlier, she arrived at the venue in a green saree and was welcomed by Tamil Nadu Chief Secretary Gnanadesikan with a bouquet.
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The swearing-in ceremony was attended by BJP leaders including Union Minister Pon Radhakrishnan and national office bearer of the party H Raja.
Actors Rajinikanth, Sarathkumar and eminent music composer Ilayaraja were among the long list of dignitaries who attended the function.
Jayalalithaa was disqualified following her conviction in the Rs 66.66 crore disproportionate assets case by a trial court in Bengaluru on September 27. The Karnataka High Court had subsequently acquitted her of the charges on May 11.