The complex of N,N′‐bis‐1‐(carboxy‐2‐mercaptoethyl)ethylene‐diamine (EC) labelled with reduced Tc‐99m was proposed as a new agent in renal tubular secretion studies. Here we present the synthesis and single‐crystal X‐ray structure determination of the N,N′‐bis‐1‐(1‐carboxy‐2‐mercaptoethyl)ethylene‐diamine oxotechnetium(V) complex, [99TcO (EC)]. Crystals are orthoro‐bic, space group P212121, with a=19.570(1), b=10.080 (1), c=6.300 (1)A, Z=4 and R=0.0294. The technetium is hexacoordinated being bonded to oxygen (1.657(3)A), the two N atoms and the two deprotonated S atoms. The sixth site, trans to the oxo‐group is occupied by one deprotonated carboxylate group. The infrared spectra is also presented.