The atomic structure of a pristine (undoped) boundary in strontium titanate has been investigated using transmission electron microscopy techniques. Results of electron diffraction studies indicate a pure tilt boundary with a common \001] tilt axis, and a tilt angle of 36.8°, which corresponds to a Σ-= 5 grain boundary in the Coincidence Site Lattice (CSL) notation. High Resolution Transmission Electron Microscopy (HRTEM) indicates a symmetric tilt grain boundary with a (130) type grain boundary plane. No cation non-stoichiometry or impurity segregants could be detected at the interface, within the limits of the Energy Dispersive X-ray microanalysis technique used. The grain boundary has a compact core, with negligible planenormal rigid body translation (RBT). An in-plane RBT of (1/2)d130 (˜ 0.62 A°) was identified from the high resolution electron micrographs. An empirical model of the relaxed atomic structure of the grain boundary is proposed.