The Battle of Bang Bo, known in China as the Battle of Zhennan Pass (Chinese: ), was a major Chinese victory during the Sino-French War (August 1884 April 1885). The battle, fought on 23 and 24 March 1885 on the Tonkin-Guangxi border, saw the defeat of 1,500 soldiers of General Franois de Ngrier's 2nd Brigade of the Tonkin Expeditionary Corps by a Chinese army under the command of the Guangxi military commissioner Pan Dingxin ().The battle set the scene for the French retreat from Lng Sn on 28 March and the conclusion of the Sino-French War in early April in circumstances of considerable embarrassment for France.

The Sino-French War (traditional Chinese: 中法戰爭; simplified Chinese: 中法战争; pinyin: Zhōngfǎ Zhànzhēng, French: Guerre franco-chinoise, Vietnamese: Chiến tranh Pháp-Thanh), also known as the Tonkin War and Tonquin War, was a limited conflict fought from August 1884 to April 1885. There was no declaration of war. Militarily it was a stalemate. The Chinese armies performed better than its other nineteenth-century wars, and the war ended with French retreat on land. However, one consequence was that France supplanted China's control of Tonkin (northern Vietnam). The war strengthened the dominance of Empress Dowager Cixi over the Chinese government, but brought down the government of Prime Minister Jules Ferry in Paris. Both sides ratified the Treaty of Tientsin. According to Lloyd Eastman, "neither nation reaped diplomatic gains."