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The purpose of this experimental work is to study lean premixed fuel/air swirl flames in order to identify the factors governing flame stabilization. The experimental burner is composed of a cylindrical quartz combustion chamber (200´80mm) placed in a pressurized and cooled casing with three large optical accesses. Downstream, a converging nozzle with variable section allows to rise the pressure inside the combustion chamber up to 8 Bar. The combustion air can be preheated up to 500°C. The fuel/air injector is a radial swirler injector. The premix tube is a 70mm length and 10 mm diameter cylinder. The experimental device can operate either with natural gas or with liquid n-heptane, since liquid fuel prevaporization is to be studied in a second step. Results of the present study only concern natural gas combustion. Velocity field is measured by LDV technique, reacting zone is visualized by CH chemiluminescence imaging, mixing in the non reacting zone is qualified by acetone-PLIF, and dynamic pressure sensors are used. For the two tested swirl numbers and for a fixed inlet velocity, a Corner Recirculation Zone (CRZ) can be observed in LDV results for the non reacting flow. However the Inner Recirculation Zone (IRZ) appears only for high swirl numbers. For atmospheric pressure and Tinlet air = 20°C, a lifted flame with an unstable position is observed. The IRZ strongly decreases lift height and extends burner lean operating limit. When equivalence ratio is decreased, instability intensity increases and a frequency appears at 240Hz in pressure spectrum. A cyclic evolution along pressure cycle is observed for the structure and the reaction intensity of flame foot