Fibers are important microstructural elements in many foods. The main objective of this research was to produce calcium alginate fibers with uniform diameters (about 300 and 550 μm) using a microfluidic device (MFD) and to study the effect of concentration of sodium alginate [Alg] and calcium chloride [CaCl 2] on their mechanical properties (MP). Moisture content (MO) and MP as maximum tensile stress (σ max), tensile strain at break (ΔL/L 0) and apparent Young's modulus (E) of fibers were determined and a statistical model and surface responses were developed as a function of [Alg] and [CaCl 2]. As [CaCl 2] increased first a strengthening and then a weakening of fibers were observed. Furthermore, σ max increased with the addition of Ca 2+ and a maximum of σ max was obtained for a [CaCl 2] around 1.4% (exceeding several times the stoichiometric requirements of the carboxylate groups of the polymer). Such behavior prompted a molecular explanation of what happens during gelation based on the "egg-box model" and this model is tried to complete. Moreover, fibers with [Alg] ≥1.8% showed high extensibility (ΔL/L 0 around 100%) and low values of MO. High values of E (∼0.5 MPa) were obtained for [CaCl 2] close to 1.4%. A greater understanding is needed of the interaction between cation- polysaccharide-water, taking into account [Alg] and [CaCl 2] to predict the mechanical behavior of fibers. Calcium alginate fibers are important in food engineering as texture and microencapsulation agents. © 2012 Elsevier Ltd. All rights reserved.