【Objective】The accumulation of nanoplastics (NPs) in soils poses potential threats to earthworm health. As key indicator species in soil ecosystems, earthworms play a crucial role in assessing the ecological risks associated with soilborne NPs. However, the quantification of NPs in complex biological and environmental matrices has remained a major challenge, limiting progress in this research field. Therefore, a comprehensive understanding of the absorption and excretion process of NPs by earthworms is essential for accurate exposure risk assessment.【Method】In this study, europium-labeled polystyrene nanoparticles were utilized as model NPs to quantitatively investigate the absorption, distribution, and excretion kinetics of NPs in earthworms. The organisms were exposed to the nanoparticles via three distinct administration routes: topical application onto the epidermis, direct injection into the body cavity, or introduction into the soil medium with or without oral exposure restriction (mouth sealing).【Result】Skin exposure experiments demonstrated that NPs were capable of penetrating the earthworm epidermal barrier, with absorption kinetics exhibiting a biphasic pattern: an initial rapid phase (0-3 h), primarily driven by concentration gradient–mediated passive diffusion, followed by a slower phase (3-24 h), significantly impeded by the resistance of the epidermal mucus layer and NP aggregation. Body cavity exposure studies revealed that NPs excretion via the skin also followed a biphasic pattern, characterized by rapid clearance (28.7% ± 1.4% within 3 h) and subsequent slow attenuation. The skin exudation rate was markedly lower than the penetration rate, indicating that the skin predominantly functions as an absorptive interface during NPs metabolism. Integrated sealing experiments further clarified the time-dependent shift in NPs uptake pathways: cutaneous absorption dominated during the early exposure phase (<3 h), accounting for 70.3%, whereas dietary intake became predominant after 24 h, contributing 62.5%. Notably, dermal penetration efficiency exhibited a clear dose-dependent trend, with NPs displaying organ-specific accumulation patterns in earthworms, the intestine being the primary target organ. These findings demonstrate that nanoscale plastic particles are capable of traversing the epidermal barrier of earthworms, undergoing trans-epidermal transport from the outer layer to internal tissues, as well as retrograde exudation from the inner epidermis. The significantly higher skin penetration rate compared to the exudation rate suggests that the epidermis primarily functions as an absorptive interface during NPs metabolism. Under conditions of reduced or ceased feeding activity, dermal absorption emerges as the predominant pathway for NPs uptake and accumulation in earthworms, which can be attributed to the prolonged dermal exposure to NPs in the surrounding soil environment.【Conclusion】This study highlights dermal penetration as a critical yet previously underestimated route for the uptake of NPs in earthworms, thereby providing a robust scientific basis for refining ecological risk assessment models of soilborne nanoparticles. It also contributes valuable theoretical insights into the biogeochemical cycling of NPs within soil ecosystems.