This paper describes a multi-probe method for measuring the straightness error of a leadscrew-driven stage. Two displacement probes are employed to scan a flat artifact mounted on the stage. The surface profile error of the flat artifact is separated from the straightness error of the stage in a differential output of the probes. The straightness error can thus be obtained accurately from an integration operation of the differential output without the influence of the surface profile error. An improved technique of data processing is adopted for measurement of straightness error components with periodicity shorter than the probe spacing. The influence of the angular error of the stage is compensated for by using the result measured by an autocollimator. Experiments of straightness measurement of a leadscrew-driven stage with a lead of 1 mm were carried out by using two flat artifacts with different degrees of precision. The successful detection of the short-periodicity component of the straightness error with a periodicity equal to the lead indicated the feasibility of the multi-probe method.