Julio Walter Montero Castillo (born 25 April 1944) is a Uruguayan former professional footballer who played as a defender.
Born in Montevideo, Montero Castillo started his career with Liverpool FC (Montevideo), before joining Nacional in 1966. He later played for Independiente of Argentina, and Spanish side Granada. He made 64 La Liga appearances for Granada between 1973 and 1975, scoring two goals.
He made a total of 68 Copa Libertadores appearances between 1966 and 1973.
He represented the Uruguay national team in the 1970 FIFA World Cup (playing in all six matches) and the 1974 FIFA World Cup. He 44 appearances in total, scoring one goal.
Montero Castillo is the father of the international footballer Paolo Montero.