National Route 170 is a national highway of Japan connecting Takatsuki, Osaka and Izumisano, Osaka in Japan, with a total length of 74 km (45.98 mi).

Route 170 was originally designated on 18 May 1953 from Wakayama to Matsusaka (this was Route 41 from 1945 to 1953).

After it was extended to Tsu, the route was redesignated as Route 42 on 1 April 1959.

On 1 April 1982 the terminus was moved from Hashimoto to Izumisano.

This article relating to the roads and highways in Japan is a stub.