Proceeding of the Joint International Symposium on Deformatuon Monitoring. 2-4 November, 2011. Hong Kong. China. Report. Measurement of deflections of railway bridges when they are crossed by trains is important for the design and evaluation of their structural health. In this paper are presented the results of RTS monitoring of the Gorgopotamos Railway bridge in central Greece, a bridge >100 years old with several openings of ~30m. This bridge was partly destroyed and rebuilt twice, and its dynamic behavior is practically unknown.Our study focused on the apparent vertical displacements of a reflector set at the midspan of an opening, where maximum displacement was expected, during the passage of trains. A high-rate robotic theodolite (RTS) with upgraded software to record measurements with centi-sec resolution was used. Based on measurements before and after the train passage, i.e. on intervals during which no deflections were expected, the noise level of the vertical deflection was estimated ~1mm. On the contrary, deflections of 6-7mm were observed when trains were passing from the bridge span. The deflection signal was analysed into a semi-static deflection of ~3mm corresponding to the bending of the span during the train passage and an oscillation of ~4-5mm, corresponding to dynamic deflections caused separately by each passing wagon. Obtained results are statistically significant, permit even estimation of reliable spectra of the displacements and consistent with theoretical models. Hence they show the potential of RTS in structural health monitoring.