The field of smart textile actuators has been progressing rapidly during the last years. Smart textiles are a class of textile products which exploit the determinant feature of responding to a stimulus, input, which can be chemical, mechanical, optical, magnetic or electrical. The building block for fabrication of such products is smart yarn. However, most smart textiles are focused on receiving an input stimulus (sensors) and only a few are dedicated to providing an output response (actuators). Yarn actuators show strain or apply force upon application of electrical stimulation in isotonic or isometric conditions, respectively. A small actuation in the yarn scale can be amplified by knitting or weaving the smart yarns into a fabric. In this work, we have investigated the effect of inherent properties of different commercial yarns on the linear actuation of the smart yarns in aqueous media. Since actuation significantly depends on the structure and mechanical properties of the yarns, elastic modules, and tenacity of the yarns were characterized. Investigating the actuation behavior, yarns were coated with PEDOT:PSS to make them conductive. Then polypyrrole which provides the electromechanical actuation was electropolymerized on the yarn surface under controlled conditions. Finally, linear actuation of the prepared smart yarns was investigated under aqueous electrolyte in both isotonic and isometric conditions.