Four new secoiridoids, syrretoside A (1), syrretoside B (2), 5β, 8β-syrretaglucone C(3), 5β, 8α-syrretaglucone C (4), together with eight known secoiridoids (5–12), were isolated from the stem barks of Syringa reticulata (Bl.) Hara. The structures of isolated compounds were established based on the physical and chemical means, NMR spectroscopy, high-resolution mass spectrometry (HR-ESI-MS), and circular dichroism spectrum (CD), as well as in comparison with the literature. The cytotoxicity of isolated compounds was investigated using CCK8...