Volunteer participation benefits societies and individuals. The objective of this study was to examine the roles of education and adult literacy in formal volunteering among a nationally representative sample of the U.S. middle-aged and older adults (45-74 years) by race and ethnicity (Whites, Blacks, Hispanics). Using cross-sectional data (n = 3,770) from the 2012/2014/2017 Program for the International Assessment of Adult Competencies (PIAAC), structural equation models were used to determine mediation relationships among educational attainment, literacy, and volunteering. The effect of educational attainment on formal volunteering was significantly greater among middle-aged and older Black adults compared to their Hispanic counterparts, as well as among middle-aged and older White adults compared to their Hispanic counterparts. However, literacy was the education-volunteering mediator among White adults only. Suggested policy implications include support for volunteer participation through culturally and socioeconomically sensitive approaches along with human capital development in adult life stages. [This paper was published in "Educational Gerontology" Oct 2022.]