Background and Aims: AMP-activated protein kinase (AMPK) is a heterotrimeric complex composed by one catalytic (alpha) and two regulatory subunits (beta and gamma). AMPK, which acts as an energy sensor that helps to maintain the energy balance in the cell, is activated when the cell’s levels of AMP rises and ATP is depleted. Trans-differentiation of quiescent hepatic stellate cells (HSCs), into extracellular matrix producing, proliferative and contractile myofibroblast-like cells (activated HSCs) is a complex mechanism which could need amounts of energy. Here we evaluated the expression and activity of AMPK during the activation processes of HSC, the impact of AMPK catalytic subunit alpha1 (AMPKa1) deletion and AMPK activation on the HSC trans-differentiation. Methods: Primary HSCs were isolated from Balb/C and AMPKa1−/− mice. AMPK activation has been obtained by incubation of primary HSCs with the adenosine analog 5-aminoimidazole-4-carboxamide-1-b-Dribofuranoside (AICAR) during 48 hours. Total, alpha1 and alpha2 AMPK activity, AMPK subunits mRNA and protein expression and Collagen-Ia1 mRNA expression were measured to asses impact of AMPK during HSC activation. a-Smooth-muscle actin (aSMA) and phalloidin, which binds specifically at the interface between F-actin subunits, expression have been visualized by immunochemistry to evaluate the impact of AMPK activation or deletion on HSC morphology. Results: AMPK activity is significantly increased in primary HSCs during time in culture. This has been confirmed by the protein expression of the phosphorylated-form of AMPK (activated form). However, only the mRNA expression of the regulatory gamma3 subunit, implicated in the AMPK complex stability, is increased in culture. AMPKa1 catalytic subunit deletion seemed to alter the HSC’s morphology without affecting their activation. AMPK activation by treatment with AICAR decreased significantly Collagen mRNA expression. Conclusion: Our data demonstrate for the first time that HSC transdifferentiation is associated with an increase of AMPK activity, probably related to increased expression of AMPKg3 and stabilisation of the complex. The absence of the alpha1 subunit appears to alter the cell morphology, but not their activation. By contrast, activation of total AMPK inhibits the HSC activation. Thus AMPK plays a role in the control of HSC phenotype and trans-differentiation but the mechanisms implicated remains to be elucidated.