| Country: | TWN |
| Type: | PH |
| Route: | 78 |
| Established: | 6 February 2002 |
| Alternate Name: | 台西古坑線 (Taixi-Gukeng Expressway) |
| Length Km: | 42.879 |
| Map: | TW_PHW78route.svg |
| Direction A: | West |
| Terminus A: | in Taixi, Yunlin |
| Junction: | in Dounan, Yunlin |
| Direction B: | East |
| Terminus B: | in Gukeng, Yunlin |
| Previous Type: | PH |
| Previous Route: | 76 |
| Next Type: | PH |
| Next Route: | 82 |
Provincial Highway 78 begins in Taixi, Yunlin, Taiwan, on Zhonghua Road (Provincial Highway No. 17) and ends in Gukeng, Yunlin on National Highway No. 3.
The total length is 42.879 km.
The entire route is within Yunlin County.