<p>The combination of optical fiber and phototheranostic agents has emerged as a promising strategy to address the challenges of limited light penetration depth and systemic toxicity of nanomaterials. However, the multiplexing potential of fiber-optic probes remains underrated, resulting in enlarged incisions, repeated invasive procedures, and a lack of real-time therapeutic feedback. Herein, we propose a scheme for single‑fiber multifunctional integration leveraging wavelength division multiplexing technology. As a proof-of-concept, by co-immobilizing pH indicator, temperature indicator, and photothermal agent with non-overlapped excitation bands onto tapered optical fiber surface, a fiber-optic theranostic probe enabling closed-loop tumor photothermal therapy was developed. Pre-treatment, the probe can achieve tumor edge identification through revealing the tumor pH gradient. Intra-treatment, the photothermal agent can convert optical energy into heat for photothermal therapy, while simultaneous temperature monitoring enables precise thermal dose control. Post-treatment, rapid efficacy assessment can be achieved via real-time monitoring of the reversal of acidic tumor microenvironment. Animal experiments validate the excellent therapeutic efficacy and biocompatibility of the probe. This research opens new avenues for multifunctional fiber-optic theranostic platforms, where modular wavelength assignment enables customizable minimally invasive interventions and feedback monitoring, holding significant promise for both clinical practice and mechanistic exploration.</p>