Background Hospital cleaners are the unsung heroes in the fight against the COVID-19 pandemic. This study aims to assess the knowledge, attitudes, and practices (KAP) of hospital cleaners towards COVID-19 and to determine factors associated with good practices. Methods A cross-sectional study was conducted in Lebanon between 1st and 14th November 2020. Data was collected through an online survey that was sent to governmental-run and private hospitals. The questionnaire consisted of socio-demographic characteristics, clinical information, and KAP of hospital cleaners towards Covid-19. The collected data was exported to SPSS for analysis. The relation between nominal variables was tested using the chi-squared test. The variables in bivariate analysis with p-value<0.2 were entered into multivariable logistic regression. Adjusted odds ratio and their 95% confidence intervals were reported. The level of statistical significance was set at a p-value < 0.05. Results A total of 453 cleaners completed the survey of which 54.3% were females. Most of the participants had a good level of COVID-19 knowledge (98%) and good preventive practices (89.7%). Regarding attitude, 90.7% had a positive attitude toward health facilities, 78.8% towards cleaning and disinfection, and 73.5% towards health authorities. Sociodemographic characteristics including younger age, higher levels of education, working in private hospitals, and having more than 3 years of experience were positively associated with good preventive practices. Our results also showed that participants with good knowledge about COVID-19, COVID-19 prevention and treatment, cleaning and disinfection process, and COVID-19 risk factors had a higher likelihood of positive preventive practices. Finally, a positive attitude towards health facilities, health authorities, and cleaning and disinfection were positively associated with good practices. Conclusion Our results indicate that cleaners have a high level of knowledge, expressed positive attitudes towards health facilities and health authorities, and good preventive practices. Understanding the determinants of cleaning performance is critical in tailoring interventions to improve hospital cleaning.