The effects of the coronavirus disease 2019 (COVID-19) are not only limited to health, they also impinge on the social life and economy of communities around the globe. Challenges faced by developing countries such as Bangladesh were multi-factorial and its rural population was highly vulnerable in this situation due to their cultural and sociodemographic context. Preventive behavioral changes were considered the best way to fight against the virus in absence of specific treatment and vaccines. This study has tried to explain preventive health practices during the COVID-19 pandemic, and aimed to explore the causal relationships of its major determinants through structural equation modeling (SEM) based on reasoned action approach (RAA). This cross-sectional study was conducted in 2020 among 810 rural Bangladeshi respondents aged 18-55 years. Around half of the respondents showed poor knowledge, motivation and practice regarding COVID-19 and its prevention. Along with socio-demographic factors, information, attitude, motivation, and intention of the people were found to be associated with the adoption of preventive health practices. The causal model of the COVID-19 prevention behaviors was assessed and justified through SEM. The model fits well with the empirical data (GFI=0.94, CFI=0.97, NFI=0.97, RMSEA=0.05, SRMR=0.04). Intention significantly influenced COVID-19 prevention behavior directly, showing the highest effect (β=0.89, p<0.001). Attitude (β=0.83, p<0.001) and motivation (β=0.15, p<0.001) also showed significant direct effects on intention. All the predictors together explained 79.6% of the variance for COVID-19 preventive behaviors. Adequate knowledge, a positive attitude, proper motivation, and positive intention can encourage rural adults to adopt healthy behaviors against COVID-19. The theoretical model of the study effectively explained COVID-19 preventive behaviors rationally and provided a roadmap for policy-makers to formulate strategies to combat COVID-19 and any future similar pandemic.