The Llanidloes and Newtown Railway (L&NR) was a railway company between Llanidloes and Newtown in Montgomeryshire, Wales. It was promoted locally when plans for trunk railways passing through the locality were cancelled; local people saw that a railway connection was essential to the flannel industry in the district. The 17-mile (27 km) line opened in 1859, and at first was isolated from any other railway, but from 1861 it became connected to Oswestry by an allied railway company, and other companies also connected to it. From 1864 the company was incorporated into the new Cambrian Railways company.
Serving a thinly populated and remote area, the line was never commercially successful, and the long-distance through routes passing through did not succeed in bringing great traffic volumes to the line. When Llanidloes station was to be extended and improved, the Manchester and Milford Railway (M&MR), then under construction, undertook to pay a one-third share of the cost of the works, and of future maintenance and operation of the station. The M&MR later decided to alter the course of its line and never reached Llanidloes, but continued to be liable for heavy charges for a station it did not connect with.
Major route closures took place in the region in the 1960s, but a portion of the L&NR, from Newtown to Moat Lane, continues in use, carrying passenger trains on the Shrewsbury to Aberystwyth line.