The objective of this study is to characterise the two-phase flow hydrodynamic behaviour of a rectangular air-lift loop reactor. The local and global gas hold-up, the global liquid circulation velocity, and the bubbles diameter, were measured and correlated to the superficial gas velocity or the pressure drop created by the gas sparger. The influence of geometrical and operating parameters was also studied. Then, a mathematical model was developed to predict the average gas hold-up (respectively, in the riser and the downcomer), and the global liquid circulation velocity. It was validated with experimental data.