A total of 17 low-cost single-frequency L1 global positioning system (GPS) receivers with real-time internet transmission have been set up to intensify the pre-existing network of continuously operating reference stations (CORS) in southeastern Taiwan since 2008. The main objective of this study is to investigate the validity and uncertainty of the L1 stations in southeastern Taiwan. It is well known that the main error source of single-frequency GPS relative positioning in low latitude areas comes from an atmospheric delay, even if the relative distance is only a few kilometres. In this study, two methods of correction algorithms, including adopting local ionospheric models and applying correction terms from local CORS, are tested to estimate the long-period accuracy of station positioning. Our results indicate that the standard deviation of calibrated relative positioning is in a linear trend with respect to the baseline length. The derived positioning accuracies from applying correction terms from CORS provide satisfactory results with the linear ratios of standard deviation/baseline of 0.11¡0.02, 0.12¡0.02, 0.44¡0.06 mm km -1 in the north, east and up component, respectively for relative distances under 30 km. The corresponding positioning scatterings amount to 3, 3 and 13 mm, in the north, east and up component, respectively. Although the use of a local ionospheric model algorithm can significantly reduce positioning variation, especially in the north component, the use of the correction terms method yields the best positioning results for three components, horizontal and vertical.