The National Anti-Corruption Commission found the senators had "misused their authority in violation of the constitution" and will forward the case to the Senate, commission Secretary-General Sansern Poljiak said.
The 36 senators will be suspended from their jobs while the Senate decides whether to impeach them, although most will be replaced by recently elected lawmakers next month.
The indictment is the latest in a series of legal challenges that caretaker Prime Minister Yingluck Shinawatra and her Pheu Thai party-led government have been battling since the lower house was dissolved in December.
The indicted senators were among 308 current and former lawmakers charged by the anti-graft body for voting last year for a bill that would have changed the composition of the 150-member Senate, about half of which is appointed. The commission had previously indicted the House and the Senate speakers on charges of mishandling the parliamentary meetings on the charter amendment.
Also Read
The bill was passed by the ruling party-controlled Parliament but was struck down by the Constitutional Court in November.
The commission is one of several nominally independent agencies which belong to the executive branch but function outside the Cabinet's authority. It has powers to investigate and prosecute elected politicians and civil servants.