1978 King Cup
The 1978 King Cup was the 20th season of the knockout competition since its establishment in 1956. Al-Ahli were the defending champions and successfully defended the title, winning their second one in a row. Al-Ahli beat Al-Riyadh who became the first Prince [Mohammad bin Salman League|First Division] side to reach the final.
By winning both the 1977–78 Saudi Premier League and the 1978 King Cup, Al-Ahli became the first Saudi team to achieve the domestic double.
Bracket
Source:Round of 32
The matches of the Round of 32 were held on 30 and 31 March 1978.| Home team | Score | Away team |
| Al-Nassr | 3–0 | Al-Shate'e |
| Al-Ittihad | 2–0 | Al-Jabalain |
| Al-Tai | 1–0 | Okaz |
| Hajer | 2–1 | Al-Taawoun |
| Ohod | 7–0 | Al-Fayha |
| Al-Qadsiah | 2–0 | Al-Shoulla |
| Al-Ahli | 9–0 | Al-Jazeera |
| Al-Nahda | 4–0 | Al-Majd |
| Al-Riyadh | 3–0 | Al-Nakhil |
| Al-Wadea | 9–0 | Tuwaiq |
| Al-Rabe'e | 2–3 | Al-Hada |
| Al-Wehda | 6–0 | Al-Kawkab |
| Al-Ettifaq | 14–1 | Al-Tadamon |
| Al-Shabab | 4–1 | Al-Khaleej |
| Al-Hilal | 2–1 | Al-Arabi |
| Al-Ansar | 4–0 | Damac |
Round of 16
The Round of 16 matches were held on 5 and 6 April 1978.| Home team | Score | Away team |
| Al-Hilal | 1–2 | Al-Qadsiah |
| Al-Ittihad | 1–0 | Ohod |
| Al-Ettifaq | 4–0 | Al-Wadea |
| Al-Wehda | 6–0 | Al-Hada |
| Al-Shabab | 1–0 | Hajer |
| Al-Nahda | 2–2 | Al-Tai |
| Al-Ansar | 2–3 | Al-Riyadh |
| Al-Ahli | 1–0 | Al-Nassr |
Quarter-finals
The Quarter-final matches were held on 11 and 12 April 1978.| Home team | Score | Away team |
| Al-Nahda | 1–0 | Al-Ettifaq |
| Al-Ittihad | 1–3 | Al-Qadsiah |
| Al-Ahli | 3–0 | Al-Wehda |
| Al-Riyadh | 1–1 | Al-Shabab |