The Wu dialects of the Chinese language (吳方言 pinyin wu fang yan; 吳語 pinyin wu yu) are spoken in the provinces of Jiangsu and Zhejiang. Wu includes Shanghainese, Suzhou, Wenzhou, Hangzhou, Yongkang and Shaoxing dialects. As of 1991, there are 87 million speakers of Wu Chinese, making it the second largest form of Chinese after Mandarin (which has 800 million speakers).

See language tree of the Chinese dialects starting from 1500 BC, and Wu's position relative to them.

Wu dialects are notable among Chinese dialects in having kept voiced consonants, such as /b/, /d/, /g/, /z/, /v/, etc. (These may in fact be better described as voiceless consonants that create a voiced breathy element across the syllable: i.e. /p\/, /t\/, etc). Neither Mandarin nor Cantonese have voiced consonants. Differences in grammar also exist. Wu dialects have a relatively higher amount of Subject-Object-Verb sentence structure than Mandarin or Cantonese. There is huge array of personal and demonstrative pronouns used within the Wu dialects. Sandhi is also extremely complex, and helps parse multisyllabic words and idiomatic phrases. In some cases, indirect objects are distinguished from direct objects by a voiced/voiceless distinction.

It is thought that there are two branches of the Wu family of dialects, northern (Jiangsu), and southern (Zhejiang), with the southern dialects often being more conservative, tonally. Much of Mandarin vocabulary is derived from northern Wu; while some modern Japanese words loaned into Mandarin also became absorbed into northern Wu. Hence today, the vocabulary used between northern Wu and Mandarin are quite similar.

The Japanese Go-on (呉音) pronounciation of Chinese characters (obtained from the Wu Kingdom during the Three Kingdoms period) is from the same region of China where Wu is spoken today.