Public service motivation (PSM) is usually measured using self-report data, which suggests that PSM measures can be influenced by social desirability bias. This study investigates whether respondents tend to report an inflated view of their attitudes and orientations during surveys on PSM. Experimental survey research (list experiment) is conducted to analyze the magnitude of social desirability bias in PSM measurements and to examine the relationship between socio-demographic factors and social desirability bias in Korea. The results show evidence of social desirability responding bias, although the pattern of bias varies across socio-demographic subgroups. Respondents in their forties or fifties, conservatives, Protestants, and those without a religious affiliation show more bias than other subgroups. This finding implies that correlational analysis in PSM research may be prone to the moderating effect of social desirability bias. Research that does not recognize and compensate for this bias may produce unwarranted theoretical or practical conclusions.