The human capital theory in economics argues that education is an investment in human capital and that the acquisition of knowledge and skills would enable individuals to increase their productivity and earnings, and thereby contributing to economic growth. As an investment, education incurs costs and benefits at various points in time. To measure economic benefits of education investment by individuals, economists use the rate of return to investment in education. This rate of return should be positive and higher than that of alternative options to ensure economic benefits of education investment and motivate education decisions. Given that tertiary education attainment is costly to individuals and the society at large, highly positive returns to tertiary education matter for individual and social human capital investments being economically justified. In the present age of mass access to tertiary education, the pattern of declining returns to investment in tertiary education was observed in a growing number of countries that include Vietnam. This trend may avert individual investment in human capital formation, and thereby negatively affecting national economic growth and development. To contribute to addressing this problem, the current paper aims to analyse the factors that drive the decay in returns to investment in tertiary education in Vietnam. Based on the descriptive research method using descriptive statistics, we summarize key trends in tertiary education in Vietnam. We identify that the abatement in returns to tertiary education investment in Vietnam may be attributed to three main factors: (i) the expansion of education supply, in particular tertiary education; (ii) the economic downturn after the global financial crisis; and (iii) the mismatched quality of tertiary education. These findings are foundations for our suggestions on possible solutions to inform the tertiary education development strategy.