Mariano Castillo Larenas (25 December 1905 – 23 September 1970) was a Chilean chess master.

Over the period of 30 years, he won nine times Chilean Chess Championship (1924, 1926, 1927, 1929, 1934, 1940, 1947, 1949, and 1953).^[1]

Castillo participated in several international tournaments where took 8th at Mar del Plata it 1928 (Roberto Grau won), tied for 6-10th at Buenos Aires 1934/35 (South American Chess Championship, Luis Piazzini won),^[2] tied for 9-10th at Mar del Plata 1936 (Isaías Pleci won), took 6th at Aguas de Sao Pedro/São Paulo 1941 (Erich Eliskases and Carlos Guimard won), took 3rd, behind Guimard and Miguel Najdorf, at Viña del Mar 1945,^[3] took 6th at Viña del Mar 1947 (Gideon Ståhlberg won),^[4] tied for 14-15th at Mar del Plata 1948 (Eliskases won), tied for 15-16th at Mar del Plata 1950 (Svetozar Gligorić won), took 9th at Venice 1950 (Alexander Kotov won), and tied for 14-15th at Mar del Plata 1954 (zonal, Oscar Panno won).

He played twice at first board for Chile in Chess Olympiads:

• In the 8th Chess Olympiad at Buenos Aires 1939 (+2 –9 =4);
• In the 9th Chess Olympiad at Dubrovnik 1950 (+3 –6 =6).^[5]