Provincial Road 421 (PR 421) is a 20.5-kilometre-long (12.7 mi) east–west highway in the Pembina Valley Region of Manitoba.

It connects Altona with Letellier and Emerson via Gnadenfeld, Neubergthal, and Sommerfeld.

PR 421 begins in the Municipality of Rhineland at a junction with PTH 30 just south of Altona.

It heads due east, travelling through the centre of both Gnadenfeld and Neubergthal before grazing along the northern side of Sommerfeld.

After crossing a bridge over the Marais River, PR 421 comes to an end a short distance later at an intersection with PTH 75 (Lord Selkirk Highway), roughly halfway between Emerson and Letellier.