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The instability of hydrothermal liquefaction (HTL) biocrude has impeded the broader utilization of fuel and chemical feedstock. In this paper, we investigated the storage stability of biocrude produced from HTL of microalgae. The biocrude showed good stability in phase homogeneity and water content, whereas the viscosity and average molecular weight increased by 48.4 and 41.9%, respectively, after storing for 12 months. Thermogravimetric analysis (TGA) and asphaltene content analysis indicated more high-boiling-point fraction, and asphaltene fraction appeared in biocrude during storage. Further elemental analysis and increased total acid numbers (TANs) demonstrated that oxidization acidic-compound-forming reactions occurred, and the gas chromatography–mass spectrometry (GC–MS) results evidenced this guess. However, the mechanism of biocrude storage instability still needs further analysis. The current biocrude assuredly requires stabilization refining for future applications.