Erhua (simplified Chinese: 儿化; traditional Chinese: 兒化; pinyin: érhuà), also called "erization" or "rhotacization of syllable finals", is a phonological process that adds r-coloring or the er (儿; 兒 [ɚ]) sound to syllables in spoken Mandarin Chinese. Erhuayin (儿化音; 兒化音) is the pronunciation of "er" after rhotacization of syllable finals.

It is common in most varieties of Mandarin as a diminutive suffix for nouns, though some dialects also use it for other grammatical purposes. The Standard Chinese spoken in government-produced educational and examination recordings features erhua to some extent, as in 哪儿 nǎr 'where', 一点儿 yìdiǎnr 'a little', and 好玩儿 hǎowánr 'fun'. Colloquial speech in many dialects especially in northern China has more extensive erhua than the standardized language. Southwestern Mandarin dialects such as those of Chongqing and Chengdu also have erhua. By contrast, many southern Chinese such as in Fujian and Guangdong who speak their own languages may have difficulty pronouncing the sound or may simply prefer not to pronounce it, and usually avoid words with erhua when speaking Standard Chinese; for example, the three examples listed above may be replaced with the synonyms 哪里 nǎlǐ, 一点 yìdiǎn, 好玩 hǎowán. Furthermore, erhua is extremely rare or absent in Mandarin speakers from Singapore and Taiwan.

Only a small number of words in standardized Mandarin, such as 二 èr 'two' and 耳 ěr 'ear' have r-colored vowels that do not result from the erhua process. All of the non-erhua r-colored syllables have no initial consonant, and are traditionally pronounced [ɚ] in Beijing dialect and in conservative varieties. In the recent decades, the vowel in the toned syllable er, especially èr, has been lowered in many accents, making the syllable come to approach or acquire a quality like ar—i.e. [äʵ]~[ɐʵ] with the appropriate tone.

In some publications, particularly those on Chinese linguistics, the 儿; 兒 in terms with erhua is written with a smaller size to distinguish its non-syllabic nature. This also distinguishes it from the same character being used as a noun meaning 'son'. This practice may have been introduced by Yuen Ren Chao. The small-sized characters have been proposed to Unicode and provisionally assigned by Unicode in 2024.

The basic rules controlling the surface pronunciation of erhua are as follows:

Following the rules that coda [i] and [n] are deleted, noted above, the finals in the syllables 伴儿 (bànr) 盖儿 (gàir) are both [ɐʵ]; similarly, the finals in the syllables 妹儿 (mèir) and 份儿 (fènr) are both also [ɚ]. The final in 趟儿 (tàngr) is similar but nasalized, because of the rule that the [ŋ] is deleted and the syllable is nasalized.

The realization of ar, i.e. the erhua of coda-less a, varies. It may be realized as [äʵ], distinct from anr and air, or it may be merged with the latter two. That is, a word like 把儿 bàr may be realized with either [äʵ] or [ɐʵ] depending on the speaker.

Because of the rule that [i] and [y] become glides, the finals of 气儿 (qìr) and 劲儿 (jìnr) are both [jɚ], and 裙儿 qúnr and 驴儿 lǘr are both [ɥɚ].