In our search for bioactive phenolics from plants, the culms of Phyllostachys bambusoides has been selected for investigation of anti-cariogenic and 1,1-diphenylpicrylhydrazyl (DPPH) radical scavenging agents based on the initial screening results. Fractionation process of n-hexane and $CHCl_3$ extracts afforded four phenolic constituents, ferulic acid (1), vanillin (2), coniferaldehyde (3), and coniferyl alcohol (4) as guided by their DPPH free radical scavenging activities. Additionally, activity-guided fractionation of EtOAc extract with anti-cariogenic activity has resulted in the isolation of coniferaldehyde (3), 2,6-dimethoxy-p-benzoquinone (5), p-methoxycinnamic acid (6), (${pm}$)-balanophonin (7), and 6-methoxychromanone (8). The structures of 1 - 8 were determined by spectroscopic data interpretation, and also by comparison of their data with the published values. Phenolic compounds 1 - 4 exhibited similar DPPH radical scavenging activities compared with the synthetic antioxidant, butylated hydroxytoluene (BHT), and compounds 3 and 5 - 8 showed significant antibacterial activity against cariogenic oral streptococci, Streptococcus mutans and S. sobrinus.