1999–2000 Tamil Nadu Legislative Assembly by-elections

By-elections to Natham and Thiruvattar constituencies were held in Tamil Nadu, India, on 5 and 11 September 1999 respectively. Elections for three state assembly constituencies, Nellikuppam, Tiruchirappalli - II and Arantangi were held on 17 February 2000.

In the first phase, TMC lost a seat to AIADMK and Dravida Munnetra Kazhagam (DMK) lost a seat to Communist Party of India (Marxist) (CPI (M)). In the second phase, AIADMK splinter party MADMK, was able to pick up a seat from AIADMK and DMK was able to hold on to its seats.

Results

 * The number on the left, in the table, represents the total number of MLAs after the by-election, and the number in parentheses represents the seats picked up or lost due to the by-election
 * The numbers presented for 1996, represents, the alliance, when the TMC and the left allied with the DMK.

Constituents and results
Source: Election Commission of India

Thiruvattar
Source: Tamil Nadu Legislative Assembly