The Air Self-Defense force scrambled fighter jets to prevent possible incursions by Chinese planes a record 117 times for the July-September period, the Defense Ministry said.
The number was up from 103 in the same period last year, although it was lower than the all-time quarterly high of 164 times recorded in October-December 2014, the ministry said Monday.
It was not immediately clear why the number of scrambles rose and the ministry did not offer an explanation.
Prime Minister Shinzo Abe and China's top diplomat, Yang Jiechi, agreed last week to push for early adoption of a communications mechanism, now in the works, to avert military misunderstandings.
Sino-Japanese ties, plagued by the dispute over the Senkaku Islands and the two countries' wartime past, concerns over Tokyo's bolder security stance and Beijing's increasing military assertiveness, have thawed a little in the last year.
Scrambles against Russian planes fell 43 percent from a year earlier to 51 times in July-September, helping bring down the number of the ASDF's overall scrambles in the three-month period by 12 percent to 170.
Russian bombers and patrol planes often fly close to Japan's northern air space close to Hokkaido and the four small islands claimed by both countries.