The ductility of HSC beams is enhanced through the application of helical reinforcement located in the compression region of the beams. The diameter and pitch of helix are important parameters controlling the level of ductility enhancement of over reinforced high strength concrete beams. This paper presents an experimental investigation of the effect of helix pitch and diameter on the beam behaviour through testing 10 helically confined full scale beams. Two groups of five beams each had exactly the same geometry and reinforcement; with the only differences being the diameter and pitch of the helices. For one group the helix was made of 8 mm diameter bars and the second of 12 mm diameter bars. The helix pitches were 25, 50, 75, 100 and 160 mm. Beams’ cross section was 200x300 mm, with a length of 4 m and a clear span 3.6 m subjected to four point loading, with emphasis placed on the mid-span deflection. The main results indicate that the helical effectiveness is negligible when the helical pitch is 160 mm (helix diameter) and the displacement ductility index increases as the helical pitch decreases. Finally, considerable displacement ductility is revealed for beams confined with 25 mm pitch helix in both the 8 mm and 12 mm helix bar diameter.