This paper presents a novel study on the analysis of the "fully compliant" spatial four-bar mechanism. To the best of our knowledge, any research on "fully compliant" spatial four-bar mechanism is not available in the literature. In the previous study performed by the authors, a "partially compliant" version of the spatial four-bar mechanism was introduced. There was a rigid spherical joint in that case, thus there was no torsional loading at flexural hinges. For the fully compliant case, there is no spherical joint in the structure of the mechanism, thereby there is also torsion available at multiple axis flexural hinges. Design of this fully compliant mechanism is different from the partially compliant case. In this study, deflections of the multiple axis flexural hinges are determined separately as bending and twist. Essential angles for manufacturing a mechanism are determined. A prototype is built and results of the mathematical model are verified with experiments. Finally, a fatigue test is performed. After one and a half million cycles it is observed that there is no indication of any failure. Since there are many applications of rigid spatial four bar mechanisms, it is strongly believed that a fully compliant version of such a mechanism may also find applications.