Biodegradable nanogenerators offer a promising route toward self-powered bio-integrated systems by converting biomechanical energy into electrical signals while safely degrading after use. Among them, triboelectric and piezoelectric nanogenerators (TENGs and PENGs) are particularly attractive for harvesting low-frequency physiological motions through soft, flexible, and bioresorbable material systems. This review summarizes recent advances in biodegradable TENGs, PENGs, and hybrid TENG/PENG systems, with a focus on energy-conversion mechanisms, material selection, device architectures, and integration strategies for wearable and implantable biomedical applications. We further discuss key challenges in performance stability, degradation behavior, biological safety, and system-level integration, and provide perspectives toward fully transient, self-powered biomedical platforms.