Abstract: A portable guardrail straightener for field use whereby damaged guardrails along highways may be straightened without the necessity of removing and retrieving the guardrails to a shop site for repair, the portable guardrail straightener for field use comprising a mechanism to be mounted on a vehicle whereby the mechanism is transported from one field location to another, the mechanism further comprising a guardrail straightening jig comprising two matching dies the configuration of which conforms to the cross section of an undamaged guardrail, one die being mounted to a reciprocable carriage driven by a two-way cylinder between open and closed positions and the other die being mounted to a fixed frame such that once the dies are located horizontally juxtaposed a damaged section of guardrail and closed, the damaged guardrail will be cold deformed into substantially its initial longitudinal and cross-sectional configuration.