A facile vapor-assisted conversion strategy has been developed to prepare mechanically robust spherical ferrierite zeolite, in which millimeter-sized commercial silica spheres doped with Na and Al were utilized as the precursor and cheap ethylenediamine (EDA) aqueous solution as the liquid phase. Characterization results demonstrated that the shape of the spheres can be well maintained after crystallization, and their interior is solid with compact crystal intergrowth. The ferrierite content in the resultant spheres can reach as high as 100%. More interestingly, the as-synthesized ferrierite spheres are Na+-free, and proton-form product can be directly obtained after simple calcination. The crystallization process of spherical ferrierite and the influence factors on the synthesis were investigated. It was revealed that control of the Na amount on the spherical precursor was critical for the crystallization, and a Na/Si ratio in the range of 0.10–0.13 facilitated the achievement of binder-free ferrierite spheres.