Most of the plastic waste polluting rivers and seas in Vietnam is single-use plastic items, of which plastic trash bags account for a large proportion. This study was conducted to determine the influence of subject norm, environmentally friendly product orientation, and knowledge about environmentally friendly products on intention to purchase biodegradable trash bags under the mediating effect of attitude toward environmentally friendly products. To achieve the research objectives, the author surveyed 449 Ho Chi Minh City households. Additionally, a structured interview questionnaire and the easy non-probability sampling approach were used to perform the survey. The data was analyzed using the SmartPLS 4.0 program. The results show that subject norm, environmentally friendly product orientation, and knowledge about environmentally friendly products all positively and significantly influence attitudes toward environmentally friendly products; attitudes toward environmentally friendly products also positively and significantly influence intentions to buy biodegradable trash bags; and attitudes toward environmentally friendly products act as a mediating factor in the relationship between subject norm, environmentally friendly product orientation, knowledge about environmentally friendly products, and intentions to purchase biodegradable trash bags. The research's consequences will are anticipated to help businesses develop sensible business plans.