Shigeta Mitsutoki who left Thailand when the surrogacy controversy erupted, sent the DNA sample voluntarily.
"A DNA test of a Japanese man involved in a surrogacy scandal in Thailand showed that he fathered 15 babies," police said.
"Thailand would seek help from foreign police experts to confirm the DNA test result," they added.
The case came to light soon after an Australian couple abandoned their baby with his Thai surrogate mother upon discovering the child had Down syndrome. They took the healthy twin of the baby back to Australia.
A police investigation found that Mitsutoki had travelled in and out of Thailand 65 times during the past two years.
Shigeta, according to sources, left Thailand for Cambodia on July 6 with a child and returned on July 27 alone.
He earlier had entered the country on March 25 via Cambodia alone and left shortly for Cambodia with a child.
Thailand's military junta has given a preliminary approval to a draft law to make commercial surrogacy a criminal offence.