Ricki Osterthun (born 2 May 1964) is a former tennis player from West Germany, who won one single title (1985, Hilversum) during his professional career.

The right-hander reached his highest singles ATP-ranking on 19 October 1987, when Osterhun became the number 58 of the world.

Result	W–L	Date	Tournament	Surface	Opponent	Score
Win	1–0	Jul 1985	Hilversum, Netherlands	Clay	Kent Carlsson	4–6, 4–6, 6–2, 6–4, 6–3
Loss	1–1	May 1986	Munich, West Germany	Clay	Emilio Sánchez	6–1, 6–3
Loss	1–2	Oct 1987	Toulouse, France	Carpet (i)	Tim Mayotte	6–2, 5–7, 6–4

Result	W–L	Date	Tournament	Surface	Partner	Opponents	Score
Win	1–0	Jun 1987	Athens, Greece	Clay	Tore Meinecke	Jaroslav Navrátil Tom Nijssen	6–2, 3–6, 6–2
Win	2–0	Oct 1988	Toulouse, France	Hard (i)	Tom Nijssen	Mansour Bahrami Guy Forget	6–3, 6–4
Win	3–0	Apr 1989	Nice, France	Clay	Udo Riglewski	Heinz Günthardt Balázs Taróczy	7–6, 6–7, 6–1

• Ricki Osterthun at the Association of Tennis Professionals
• Ricki Osterthun at the International Tennis Federation
• Ricki Osterthun at the Davis Cup