Bamboo is a fast-growing renewable bioresource. However, bamboo resources are wasted, and bamboo products release toxic gases. Bamboo biomass was therefore extracted and self-plasticized, and the immune effects of bamboo extractives were determined and investigated using nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed the following. (1) The 1H-NMR signals at ~5.5, 4-8, 7.4-10.2, and 12.22-12.37 ppm were attributed to the chemical shifts of active protons on carbons adjacent to R-OH, RAr-OH, oximes, and -COOH, respectively. This showed that there were highly reactive hydrogen atoms in bamboo benzene/ethanol extractives. The 13C-NMR spectrum gave further confirmation. (2) The extents of the effects of key process parameters were different: temperature > hot pressure > time. The optimal self-plasticizing conditions were temperature 170°C, hot pressure 9 MPa, time 40 min, and extraction of bamboo. (3) SEM, FT-IR, and XRD showed that contact and linkages among bamboo cells were significantly decreased by extractives, so the internal bond strengths of the self-plasticized samples were all higher after bamboo extraction. It was also found that the extractives created a significant barrier to bamboo self-plasticization as a result of their structure and chemical linkage reactions.