Mathias won a cap playing Right-Wing for Wales (RU) while at Llanelli RFC in the 11–6 victory over France at Cardiff Arms Park on Saturday 4 April 1970.
[3] Roy Mathias played on the wing in St. Helens' 2–25 defeat by the 1975 NSWRFL season premiers, Eastern Suburbs Roosters in the unofficial 1976 World Club Challenge at Sydney Cricket Ground on Tuesday 29 June 1976.
[5] Roy Mathias played on the wing in St. Helens' 20–5 victory over Widnes in the 1976 Challenge Cup Final during the 1975–76 season at Wembley Stadium, London on Saturday 8 May 1976.
Roy Mathias appeared as a substitute (replacing Prop Gary Bottell) in St. Helens 0–16 defeat by Warrington in the 1982 Lancashire Cup Final during the 1982–83 season at Central Park, Wigan on Saturday 23 October 1982.
The record for the most tries in a BBC2 Floodlit Trophy Final is two tries, and is jointly held by; Roy Mathias, Peter Glynn, Gerald Dunn and Stuart Wright.