Several Ti5Si3Zx compositions (Z = boron, carbon, nitrogen and oxygen) were synthesized by arc-melting. Powder X-ray diffraction indicates the materials maintain the Mn5Si3-type structure of the binary compound Ti5Si3. Calculated cell constants were correlated to ternary composition based on chemical analysis. Nitrogen and oxygen additions to Ti5Si3 promote a cell volume decrease, while boron additions promote a cell volume increase. Carbon additions cause a decrease in the a-cell constant and an increase in the c-cell constant with a concomitant cell volume increase. Room temperature X-ray single crystal structural analysis was performed on one composition for each ternary addition. Each analyzed composition has the P63/mcm space group (No. 193) with the Mn5Si3-type structure. The ternary addition occupies the normally vacant interstitial site at the center of the trigonal antiprisms of titanium (Ti2) atoms (Ti6Z polyhedra), located in chains at the corners of the hexagonal unit cell. Bonding between the interstitial atoms and the titanium (Ti2) atoms in the Ti6Z polyhedra is indicated by a decrease in the Ti2-Ti2 and Ti2-Z atomic separations.