Sony, which competes with Apple's iPod and iPhone in the portable music player market, said its copyrighted Japanese-language songs had been made available for sale on iTunes from this week.
Earlier this year, Sony Music Entertainment allowed songs by its Western artists to be sold on Apple's online store, after reportedly keeping them away for years.
Some analysts saw the latest move as part of a shift by Sony to reverse years of losses largely tied to its struggling television division.
But a Sony spokesman said its Japanese artists' debut on iTunes was held up by protracted contract negotiations, not a strategy to keep its rival from selling Sony-copyrighted music.
"We've been trying to expand our marketing channels, and Apple's iTunes is the 15th site where we provide music," he told AFP.
"We are starting now as we've completed contract terms."
Prices for the Japanese artists' songs will range from 200 yen ($2.50) to 250 yen, the spokesman added.
BCN analyst Eiji Mori said that "Sony may have changed its strategy as sales of music CDs are declining while purchases of music via online shops are increasingly common".
Sony's once-iconic Walkman music player outsells Apple's iPod in Japan, but the overall market is shrinking as more consumers use smartphones to play digital music, Mori said.
The iPod has dug into the Walkman's dominant position as Sony also faces competition in its videogame division from rivals including Japan's Nintendo and US firm Microsoft, which makes the Xbox.
Sony, which reported a smaller quarterly loss last week and said it remained on track to eke out a small full-year profit, has struggled with a strong yen, high labour costs and fierce competition from overseas rivals.