Many of these people entered Thailand in the hope of seeking employment in the US, where they have relatives, it said.
The Lao government is taking proper care of those sent back, it said.
Laos said it would only accept Hmong from Thailand until the end of the year and urged the Thai government to speed up the process.
Thai security forces will deport 4,000 more Hmong early tomorrow. More than 100 buses will transport them from Phetchabun's Khao Kho district to Laos via Nong Khai.
Police and the military are blocking mobile-phone calls in the area for security reasons.
Local Hmong-Thai villagers say they hope development assistance will eventually come to the area after the non-Thai Hmong refugees have left.