善于 is an adverb meaning 'good at' or 'skilled in' doing something. It combines the character 善 (shàn), which means 'good', 'virtuous', or 'skilled', and 于 (yú), a classical preposition that introduces the object or domain of skill — here, the activity one excels in. Though it looks like two separate words, 善于 functions as a fixed compound and always precedes a verb or verb phrase.

This expression is formal but common in both spoken and written Chinese, especially when describing personal strengths, professional abilities, or natural talents. It’s often used in self-introductions, resumes, performance reviews, or descriptions of people’s aptitudes. Unlike colloquial alternatives like 擅长, 善于 carries a slightly more refined or literary tone and is rarely used with nouns alone — it must be followed by a verb (e.g., 善于沟通, not 善于英语).