Hydrogen can represent an option for a low emission gas turbine if low NOx combustion systems are developed. This paper describes the design and the investigations carried out on a lean premixed burner 100% hydrogen supplied. An existing heavy-duty gas turbine burner was modified with a new axial swirler and a co-flow injection system. The designed prototype presents the interesting feature where the variable premixing level permits a wide-ranging case studying. The burner prototype was investigated during a test campaign performed on an atmospheric test rig. Flame control on burner prototype, fired by pure hydrogen, was achieved by managing the premixing degree and the flow velocity. NOx emissions, flash-back limit, and burner pressure drop were measured over a wide range of the main operating parameters: equivalence ratio, premixer discharge velocity and thermal input. Results of the measurements outline as higher velocity flow (depending on the burner arrangements and operating conditions) is necessary to avoid flame positioning inside the premixer duct when hydrogen is used. The best arrangement can limit the NOx emissions to 17 ppm but with an outlet velocity about 120 m/s. The numerical activity integrates the information on the flame shape, and it improves the knowledge of the NOx emissions and their chemical path. Anyway, the study confirmed the operability of the system and great perspective regarding NOx emission containment. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.