Inconsistent results published in previous studies make it difficult to determine the precise effect of consumer knowledge on their acceptance of functional foods, which were developed to improve consumers’ health status by providing adequate nutrition. We conducted a systematic review and meta-analysis by identifying and collecting relevant literature from three databases. Of the 1050 studies we reviewed, we included 40 in the systematic review and 18 in meta-analysis. Based on the focus of each included study, we operationally defined knowledge as knowledge of the functional food concept, nutritional-related knowledge, and knowledge of specific functional products. Results from the systematic review indicate that most participants from the included studies had a low level of knowledge, especially nutrition-related knowledge associated with consuming functional foods, and they were generally not familiar with the concept of functional foods. It is possible that participants’ level of knowledge was influenced by their demographic characteristics (e.g., age, gender, educational level, marital status, nationality). Results from the meta-analysis generated a summary effect size (r = 0.14, 95% CI [0.05; 0.23]), measured by the correlation coefficient r, which indicates that a small positive relationship exists between consumers’ level of functional foods knowledge and their acceptance of functional foods.