In this paper, we propose to estimate the individual incylinder air mass flow for a gasoline IC engine. In order to achieve this goal a periodic observer for a class of non-linear models in the discrete Takagi-Sugeno form is designed. The adopted framework to prove the stability of the observer is based on the Lyapunov theory and uses linear matrix inequalities (LMI) formalism. Some simulations and experimental results are provided to show the efficiency of the proposed method.