MDMK's S Joel and N Thillaiselvam, District Secretaries of Thootukudi and Kanyakumari, respectively, joined DMK in the presence of its president M Karunanidhi.
Tirunelveli Urban Secretary of MDMK, S Perumal, was among the scores of party leaders and workers who joined DMK, a party release said.
In Dravidian politics, the post of District Secretary is considered key in the orgsanisational set up.
Earlier, senior leaders of MDMK, including former party Treasurer R Masilamani, Women's Wing Leader Kumari Vijayakumar, District Secretaries of Kancheepuram and Salem, Palavakkam Somu and Thamraikannan, had walked out of the MDMK.
Vaiko had earlier dropped hints with partymen over aligning with DMK, a party he was initially a member of but parted ways with Karunanidhi in 1994 following differences.