Nalini, who hails from Bhongir in Nalgonda district in Telangana region, had quit from her post in November last year in support for a separate Telangana.
BJP state party chief Kishan Reddy welcomed her at the BJP state office on M J road here along with over 100 supporters.
Former Union Minister Bandaru Dattatreya, party's national secretary K Laxman and other leaders were present on the occasion.
Speaking to media later, Nalini said she had decided to join the party as it was committed to the cause of Telangana.
She claimed the party had assured people of the region that formation of Telangana would be announced within 100 days of its coming to power.
Nalini, who was working in the Women Protection Cell in the CID, was suspended from service by the Andhra Pradesh Director General of Police last year on charges of "grave misconduct" when she announced her support for Telangana publicly while in service.