In this work, we introduce a chitosan–Pt complex (CS–Pt) as an effective template for catalytic Pt sensitization and creation of abundant mesopores in SnO₂ nanofibers (NFs). The Pt particles encapsulated by the CS exhibit ultrasmall size (∼2.6 nm) and high dispersion characteristics due to repulsion between CS molecules. By combining CS–Pt with electrospinning, mesoporous SnO₂ NFs uniformly functionalized with the Pt catalyst (CS–Pt@SnO₂ NFs) are synthesized. Particularly, numerous mesopores with diameters of ∼20 nm form through the decomposition of CS, while a small SnO₂ grain size (14.32 nm) is achieved by the pinning effect of CS. It is observed that CS–Pt@SnO₂ NFs exhibit outstanding response (R_air/R_gas = 141.92 at 5 ppm), excellent selectivity, stability, and fast response (12 s)/recovery (44 s) speed toward 1 ppm of acetone at 350 °C and high humidity (90% RH). In addition, by applying an exponential fitting tool to experimental response values toward 0.1–5 ppm of acetone, it is estimated that CS–Pt@SnO₂ NFs can detect 5 ppb of acetone with a notable response (R_air/R_gas = 2.9). Furthermore, the sensor array based on CS–Pt@SnO₂ NFs, CS-driven SnO₂ NFs, polyol-Pt loaded SnO₂ NFs, and dense SnO₂ NFs obviously classifies simulated diabetic breath and healthy human breath by using a pattern recognition tool. These results clearly demonstrate that mesoporous SnO₂ NFs, particularly functionalized with CS–Pt templated nanocatalysts, open up a new class of sensing layers offering high sensitivity and selectivity.