The 1965–66 FAW Welsh Cup is the 79th season of the annual knockout tournament for competitive football teams in Wales.
League name pointed after clubs name.
Ten winners from the Fourth round and six new clubs.
| width=50 | Tie no | width=250 | Home | width=50 | Score | width=250 | Away |
|---|---|---|---|---|---|---|---|
| 1 | Chester (FL D4) | 4–1 | Wrexham (FL D4) |
| width=50 | Tie no | width=250 | Home | width=50 | Score | width=250 | Away |
|---|---|---|---|---|---|---|---|
| 1 | Newport County (FL D4) | 2–2 | Chester (FL D4) | ||||
| replay | Chester (FL D4) | 2–0 | Newport County (FL D4) |
| width=50 | Tie no | width=250 | Home | width=50 | Score | width=250 | Away |
|---|---|---|---|---|---|---|---|
| 1 | Swansea Town (FL D3) | 3–1 | Merthyr Tydfil (SFL) | ||||
| 2 | Bangor City (CCL) | 0–3 | Chester (FL D4) |
Replay were held at Chester.
| width=50 | Tie no | width=250 | Home | width=50 | Score | width=250 | Away |
|---|---|---|---|---|---|---|---|
| 1 | Swansea Town (FL D3) | 3–0 | Chester (FL D4) | ||||
| Chester (FL D4) | 1–0 | Swansea Town (FL D3) | |||||
| replay | Chester (FL D4) | 1–2 | Swansea Town (FL D3) |