| Conflict: | Cambodian anti-Vietnamese rebellion (1840) |
| Partof: | Vietnamese invasions of Cambodia |
| Date: | 1840–1841 |
| Place: | Cambodia, Cochinchina |
| Result: |
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| Combatant1: | Khmer anti-Vietnamese rebels Support: Rattanakosin Kingdom (Siam) |
| Combatant2: | Nguyễn dynasty (Vietnam) |
| Commander1: | no unified leader Ang Duong support: Chaophraya Bodindecha (Sing Sinhaseni) |
| Commander2: | Trương Minh Giảng Lê Đại Cương Lê Văn Đức Phạm Văn Điển Nguyễn Tiến Lâm former Cambodian queen, princes and ministers: Ang Mey Ang Em Chaofa Talaha (Lung) |
| Strength1: | Khmer rebels: Unknown Siamese: 20,000 mercenaries |
| Strength2: | Unknown |
| Casualties1: | Unknown |
| Casualties2: | Unknown |
The Cambodian rebellion of 1840 was a Cambodian short-lived anti-Vietnamese insurrection fought particularly heavily around Prey Veng and Ba Phnom.
In 1840, the Cambodian queen Ang Mey was deposed by Vietnamese; she was arrested and deported to Vietnam along with her relatives and the royal regalia. Spurred by the incident, many Cambodian courtiers and their followers revolted against the Vietnamese rule. The rebels appealed to Siam who supported another claimant to the Cambodian throne, Prince Ang Duong. Rama III responded and sent Ang Duong back from exile in Bangkok with Siamese troops to install him on the throne.
The Vietnamese were attacked from both Siamese troops and Cambodian rebels. In Cochinchina, several rebellions broke out. The main strength of the Vietnamese marched to Cochinchina to put down those rebellions. Thiệu Trị, the new crowned Vietnamese emperor, decided to a peaceful resolution. Trương Minh Giảng, the Governor-General of Trấn Tây (Cambodia), was called back. Giảng was arrested and later committed suicide in prison.
Ang Duong agreed to place Cambodia under joint Siamese-Vietnamese protection in 1846. The Vietnamese released Cambodian royalties and returned the royal regalia. In the same time, Vietnamese troops withdrew out of Cambodia. Giving Cambodians independence. Though there were still a few Siamese troops stayed in Cambodia, the Cambodian king had greater autonomy than before.