Mouthwash, which commonly contains chemical antibacterial agents, is usually used to eliminate oral pathogens and maintain oral health. Herein, we aim to develop a chitosan (CS)-based drug-free mouthwash. CS is known to have great antibacterial activity in acidic conditions, but such acidity is not suitable for practical use, especially in the near-netrual oral environment. The antibacterial activity of CS in the near-neutral conditions is still unknown. In this work, we prepared a near-neutral CS solution-based mouthwash (pH ~6.0) and investigated its antioxidant and antibacterial activity. The CS mouthwash containing 200 μg/mL and 400 μg/mL CS showed a pH value of 6.03 and great antibacterial activity against both Gram-negative Porphyromonas gingivalis and Gram-positive Streptococcus mutans (with a ~90% inhibition rate 3 h after incubation and an inhibition rate of almost 100% at 6 h). The antibacterial effects of CS mouthwash after 3 months show no significant differences compared to those 3 months ago, indicating the consistent and enduring antibacterial properties of CS mouthwash. The pH of the mouthwash also remained stable after 3 mouths. Damaged cell membranes and cell death were observed via SEM, which is considered to be the antibacterial mechanism. In addition, CS mouthwash caused no cytotoxicity to human oral keratinocytes and could protect human oral keratinocytes from damage under H2O2-induced oxidative stress. Also, CS mouthwash demonstrated the great capacity of intracellular ROS scavenging. This is the first report regarding the antibacterial and antioxidant activity of drug-free and near-neutral CS solution-based mouthwash. The oral-tolerated pH and the multiple functions of CS mouthwash give it great potential for clinical use. We will expand the study on the biofilms and compare the efficacy of CS with commercial products in the future.