The Singapore-Kuala Lumpur route is the world's busiest international air link, with seven airlines that operate up to 84 flights a day.
In second place is Hong Kong-Taipei, followed by Singapore-Jakarta.
The ranking by industry consultancy OAG, released on Thursday, is based on the number of flights between two cities in the 12 months to the end of February this year.
The Singapore-KL connection topped OAG's busiest international routes ranking with 30,537 flights, compared with 28,887 flights for Hong Kong-Taipei and 27,304 flights for Singapore-Jakarta.
While the Singapore-KL sector was the busiest for Changi Airport based on the number of flights operated, more people flew between Singapore and Jakarta during the same 12 months.
Total passenger traffic on the route was more than 4.6 million, compared with about four million for Singapore-KL.
Mr Mayur Patel, OAG's regional sales director for Japan and the Asia-Pacific, noted that 14 of the world's 20 busiest routes, including eight of the top 10, are between Asian cities.
"Given the robust expansion of air passenger travel across the Asia-Pacific and the fierce competition between carriers in the region, it is unsurprising," he said on Thursday.
Turning to airports, OAG noted that Hong Kong was the busiest Asian airport hub, featuring in six of the top 20 routes while Changi Airport featured in four.
Mr Patel said: "While this intense level of competition offers impressive flight frequencies and competitive prices for consumers, it adds pressure to the operating costs and on-time performance of carriers, and may prove unsustainable over time."
Other industry experts noted that the expansion of low-cost carriers in Asia has significantly boosted the number of air services between Asian cities, including Singapore-Kuala Lumpur and Singapore-Jakarta.
Number of passengers flying the Singapore-KL route in the 12 months to end-February this year.
Mr Brendan Sobie from the Centre for Aviation noted in a recent report that low-cost carriers in Singapore now operate a fleet of 60 aircraft - 44 from the Airbus 320 family and 16 Boeing 787s.
In 2012, they had just 37 planes in total.
Low-cost carriers currently account for about a third of the total passenger traffic at Changi Airport.
There are now 18 such airlines offering both short-and long-haul flights to and from Singapore, said Mr Sobie.