The 99 people included 25 junior high and high school students in cases including sharing sexual images of classmates with friends.
A total of 445 people were arrested or investigated in March and April in the international initiative that involved Japan, Singapore, Thailand, South Korea, Hong Kong, Brunei and Malaysia.
Japan joined the cooperative framework called Operation Cyber Guardian last year.
In Japan, police, acting on intelligence from Singapore, took action against a man suspected of making child pornography files accessible online.
Japanese police provided intelligence obtained through cyber patrol activities to overseas counterparts.
