The ionomeric electroactive polymers-metal composites (IPMC) are materials that realize bending movements in response to an electrical stimulus and can be applied to the artificial muscles development. This paper investigated the influence of the hydration level on the electromechanical behavior of Nafion based IPMC. An experimental apparatus composed by a system to measure the bending force and to control the electrical stimulus and the relative humidity around the sample was developed. The main results indicated that samples with higher hydration level produce larger bending forces, but they show a more expressive back relaxation with lower time constant. A discussion about the results considering some models described in the literature conclude the paper.