Biocompatible nanogenerators (NGs) are of vital importance for in vivo applications. In this work, Bi_5−xLa_xTi₃FeO₁₅ (x = 0, 1) nanofibers (NFs) toward wool keratin-based biocompatible piezoelectric NGs are demonstrated. The refined structure of Bi₄LaTi₃FeO₁₅ (BLTF) NFs by the Rietveld method was confirmed to be a four-layer Aurivillius oxide with an orthorhombic space group A21am. Wool keratin was extracted using the oxidizing and subsequent deoxidizing reaction process. BLTF NFs are biocompatible in a bio-environment shown here using mice pre-osteoblasts MC3T3-E1. The BLTF NF NG can generate an output voltage of 0.14 V and output current of 41 nA (with a current density of 20.5 nA cm⁻²), with quite reproducible power generation. The prominent power generation of the BLTF NF NG partly originated from the La³⁺ substitution for the A-site Bi³⁺, which decreases the number of oxygen vacancies in the perovskite layers. Furthermore, piezoelectric NFs as exceptional fillers coupled sufficient connectivity, a larger degree of crystallinity and Young's modulus of the system together in the keratin matrix also contributed to enhanced piezoelectric power generation. In addition, one mechanism responsible for the optimal BLTF NF NG was proposed. This study offers new insights into the design and application of promising lead-free biocompatible devices with better fillers.