We study the globular cluster Terzan 4 projected close to the Galactic center, by means of V, I and Gunn z Colour-Magnitude Diagrams. The images were obtained under exceptional seeing conditions (0.35"-0.55") at the ESO New Technology Telescope equipped with SUSI. We derive a reddening of E(B-V)=2.35 and a distance from the Sun d_{sun}_=8.3kpc for Terzan 4. From the similarity of the VI Colour-Magnitude Diagrams of Terzan 4 and M30, in particular the presence of a blue horizontal branch, it could be as metal-poor as [Fe/H]=~-2.0. It is therefore another blue horizontal branch globular cluster located close to the Galactic center.