It runs from Tokyo and Shinjuku to Chōshi on the Bōsō Peninsula in Chiba Prefecture.

Shiosai services operate over the Sōbu Main Line, stopping at the stations listed below.

[1][2][3] Tokyo - Kinshichō - Chiba - Sakura - Yachimata - Narutō - Yokoshiba - Yōkaichiba - Asahi - Iioka - Chōshi Shiosai services are operated using Kamakura-based 6-car E259 series EMU and Makuhari-based 10-car E257-500 series EMU formations.

[7][8] The Shiosai service was introduced from 10 March 1975 following the completion of electrification of the Sōbu Main Line in October 1974, using 9-car 183 series EMUs, replacing five of the seven daily diesel-powered Inubō (犬吠) express services that operated between Shinjuku/Ryōgoku and Chōshi.

[8] From the start of the revised timetable on 10 December 2005, 255 series 9-car EMUs were introduced on Shiosai services.