Carbon labeling facilitates the evaluation of carbon emissions throughout the entire food production process. Consumer interpretation of food labels is subject to context. We conduct an online discrete choice experiment in four Chinese cities to investigate the potential how social desirability bias (SDB) may affect consumer willingness-to-pay (WTP) for milk carbon labels. Our findings indicate that failing to account for SDB leads to skewed WTP estimates. We observe a significant presence of SDB in WTP for carbon labels, particularly among respondents under subject to injunctive social-norm treatment. Additionally, our research shows that SDB can manifest differently among consumers with varying levels of environmental commitment. This research provides crucial insights for both policymakers and marketers in food carbon labeling. It highlights the importance of considering SDB and emphasizes the necessity of developing tailored strategies across different consumer segments.