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The uncertainties in range determination depending on two-site locations for GEO satellites were calculated and shown that the uncertainty in the range depends not only on linear baseline distance between the locations but also both latitude and longitude of geographic coordinates of the sites. By taking the first observing site as fixed and changing the location of the second site, the triangulated range calculations were performed by using SGP4 orbital model and published Two-Line Elements (TLE). Additionally, as a sample of triangulated observation, the results of nearly synchronous two-site astrometric measurements of two GEO satellites, TURKSAT 3A and TURKSAT 4A, were presented. These astrometric observations were carried out in TÜBITAK National Observatory (TUG), Antalya and TURKSAT Company's site, Ankara. Although the baseline between the observatory sites corresponds to a relatively short distance of about 400 km, measured range determinations well stays under the error level expected by Choi et al. (2010). • Uncertainties of two-site astrometry of GEO satellites depend not only linear baseline but also both latitude and longitude of geographic coordinates. • Two-site astrometric observations reveal that uncertainties on range and position of GEO satellites stay under the error level expected by simulations. • It was also noticed that date of observation also affects the uncertainties of two-site astrometry of GEO objects. [ABSTRACT FROM AUTHOR]