The Saikyō Line (埼京線, Saikyō-sen^?) is a railway line between Ōsaki Station in Shinagawa, Tokyo, and Ōmiya Station in Saitama Prefecture, Japan. It is a part of the East Japan Railway Company (JR East) network. The line's name is an abbreviation of the two areas the line connects: Saitama (埼玉^?) and Tōkyō (東京^?).

At the northern end of the line, some trains continue beyond Ōmiya as far as Kawagoe on the Kawagoe Line; at the southern end of the line, many Saikyō Line trains continue onward beyond Ōsaki to Shin-Kiba on the Rinkai Line (operated by Tokyo Waterfront Area Rapid Transit). Beside the link that connects the Saikyō and Rinkai lines is the JR East Tokyo General Rolling Stock Centre that stores the rolling stock for the Yamanote Line and other types of rolling stock.

The line runs parallel to the Yamanote Line between Ōsaki and Ikebukuro, where it is formally called the Yamanote Freight Line (山手貨物線^?), and as an alternate route to the Tōhoku Main Line between Akabane and Ōmiya, where it is unofficially called the Tohoku Secondary Line (東北別線^?). The portion between Ikebukuro and Akabane is officially known as the Akabane Line (赤羽線^?). For most purposes, JR refers to all of these as part of the "Saikyō Line" when being used for Saikyō Line services.