The arrested are Song A Trang, 23, residing in Phieng Pan village, Mai Son district, and Giang A Tung, 20, in Na Nghiu commune, Song Ma district.
They were arrested in Le Hong Phong village, Na Nghiu commune, Song Ma district on June 19.
They confessed that they bought the heroin from a strange man in the border area and intended to sell to earn some profit.
The case is under investigation.
Son La borders Laos and is home to some ethnic minority groups.