| Guillermo del Castillo | |
| Birth Date: | 14 December 1963 |
| Birth Place: | Rosario |
| Ru Position: | Fly-half |
| Years1: | 1983-1999 |
| Repyears1: | 1990-1995 |
| Repcaps1: | 15 |
| Reppoints1: | 24 |
Guillermo del Castillo (born 14 December 1963 in Rosario) is a former Argentine rugby union player. He played as a fly-half.
Del Castillo played for Jockey Club de Rosario.
He had 15 caps for Argentina, from 1991 to 1995, scoring 3 conversions, 5 penalties and 1 drop goal, 24 points on aggregate. He was called for the 1991 Rugby World Cup, playing in two games and scoring 1 conversion and 2 penalties, 8 points on aggregate. He once again would be called for the 1995 Rugby World Cup but this time he didn't leave the bench.[1]