Alfonso Leng (11 February 11 1894 – 11 November 1974) was a post-romantic composer of classical music and dentist. He was born in Santiago, Chile. He wrote the first important symphonic work in Chilean tradition, "La Muerte de Alcino", a symphonic poem inspired by the novel of Pedro Prado. He composed also a number of different works including many art songs in different languages and a number of important piano pieces, like the five "Doloras" (1914), which he later orchestrated and are normally played in concerts in Chile and Latinamerica. He won the Nacional Art Prize in 1957. As dentist, he was the main founder of the Dentistry Faculty of the Universidad de Chile, and he was eventually elected as the first dean.
Leng was the nephew of composer Carmela Mackenna.