The suspects are 34-year-old Nishimura Masamori and three women in their 20s and 30s.
Police say the four brought the gold, worth about 650,000 dollars at the time, aboard a flight from Hong Kong to Tokyo’s Haneda Airport in July last year.
Authorities allege that they tried to avoid paying some 65,000 dollars in consumption tax and other levies at airport customs.
The four have admitted to charges of customs law and consumption tax law violations.
Police say the women were instructed by Nishimura to take a three-day sightseeing tour of Hong Kong.
They were later given small packets of powdered gold from another person in an apartment, before sewing them into their underwear.
Nishimura reportedly covered the women’s travel expenses, and they were supposed to be paid a reward if they succeeded in smuggling the gold into Japan.
Tokyo police believe other individuals, such as those who prepared the gold, were systematically involved.
