In view of global warming issues, the Taiwan government has implemented environmental-related policies and measures for sustainable development through promoting “carbon labeling” in recent years. Many studies related to carbon labeling have been conducted after its promotion, but the studies on the relationship of subjective knowledge or perceived knowledge on carbon labeling, perceived consumer effectiveness (PCE), and willingness to buy the products are still limited. Therefore, this study aimed to examine the relationship of subjective knowledge on carbon labeling, consumer perception, and willingness to buy carbon label products, with a case study of packaged tea products in Taiwan. The respondents were Taiwanese adults aged 18 years old and over, who have experience of buying packaged tea. The research was conducted by survey method using non-probability sampling method at convenience retail stores i.e., 7-Eleven and Family Mart. The result showed that (1) the consumers with high subjective knowledge have high willingness to purchase packaged tea products with carbon labels, consumers with high PCE have high subjective knowledge of carbon labeling, and consumers with high PCE have high willingness to buy carbon-labeled packaged tea products; (2) there is a positive linear relationship of subjective knowledge and PCE toward purchase intention of carbon label; and (3) a significant positive correlation between subjective knowledge, PCE, and willingness to buy packaged tea beverage products with carbon labels for the female respondents.