| Country: | TWN |
| Type: | PH |
| Route: | 66 |
| Alternate Name: | 東西向快速公路觀音大溪線 (East-West Expressway, Guanyin-Daxi Line) |
| Established: | 20 January 2001 |
| Length Km: | 27.259 |
| Map: | TW_PHW66route.svg |
| Direction A: | West |
| Terminus A: | in Guanyin |
| Junction: | |
| Direction B: | East |
| Terminus B: | in Daxi |
| Previous Type: | PH |
| Previous Route: | 65 |
| Next Type: | PH |
| Next Route: | 68 |
Provincial Highway 66 is an expressway, which begins in Guanyin District, Taoyuan City on Provincial Highway 61 and ends in Daxi District, Taoyuan City, on County Road 112A.