<p>Monitoring biochemical oxygen demand (BOD) decay offers critical insights into the aerobic biodegradation of dissolved organic matter (DOM). Focusing on the accumulated metabolites generated during DOM biodegradation, this study introduces novel fluorescence parameters that facilitate the rapid monitoring of BOD decay throughout the entire DOM degradation process until BOD is depleted. BOD decay during degradation of four synthetic DOM samples was first investigated (initial BOD &lt; 10 mg/L) and showed a S-shaped decay pattern with excellent goodness of fit (<i>R</i>² &gt; 0.93; <i>p</i> &lt; 0.001). In contrast, critical spectral signals intensified also in the S-shaped pattern, of which the transition phase converged temporally with BOD decay (time difference &lt; 0.7 d), demonstrating that chromophore-bearing metabolites accumulated synchronously with BOD decay. Pearson analysis further corroborated the highly significant correlations between BOD and spectral signals derived from metabolites throughout the process of DOM degradation. According to Pearson analysis, three metabolite-derived fluorescence parameters were yielded based on three newly specified fluorescence regions related to metabolites (mean <i>r</i> ≈ −0.70; <i>p</i> &lt; 0.05). With a real water sample, we confirmed that these metabolite-derived fluorescence parameters outperformed traditional fluorescence parameters in tracking BOD decay, with a higher <i>R</i>² in multiple linear regression (<i>R</i>² &gt; 0.8; <i>p</i> &lt; 0.001). The findings present a promising approach for rapid tracking and early warning of BOD decay during DOM degradation, potentially contributing to water quality management.</p>