The airline has also frozen its intake of cadet pilots as part of a slew of cost-cutting measures.
"Singapore Airlines (SIA) began offering voluntary no-pay leave to first officers in March last year and subsequently to captains who expressed interest," company spokesman Nicholas Ionides said in a statement emailed to AFP.
SIA has "a temporary surplus of pilots and are managing it through this scheme, which is entirely voluntary", Ionides said.
He added that "the surplus of captains is limited and we regard it as temporary".
SIA has more than 2,400 pilots -- mostly captains and first officers.
The global financial crisis had led to excess capacity and slower growth that anticipated, Ionides said.
"This voluntary scheme will enable us to address the short-term surplus, while at the same time provide staff with the opportunity to take leave for personal reasons should they wish to do so," he said.
SIA saw its net profit in the first-half of the current fiscal year ending March fall by 30 percent year-on-year, weighed down by high fuel prices and weak demand in the travel and cargo markets.
This followed a 69% plunge in net profit in the carrier's financial year ended March 2012.