The reliability of surface electromyographic (sEMG) variables during swallowing determines the potential usefulness of these measures in swallowing assessment and treatment. This study aimed to establish the reliability of the sEMG measures of the swallowing function of muscles during different swallowing conditions in healthy young and old volunteers. Two groups of volunteers (24 older adults, 10 younger adults) participated in this cross-sectional study during 2014. The activity of masseter, submental, and infrahyoid groups were measured using sEMG during three repetitions of different swallowing tasks. Both the relative and absolute reliability (characterized respectively by ICC, SEM%, and SRD%) were calculated for the sEMG indices of muscle activity during swallowing events. Statistical analyses were performed by the SPSS 19.0 and Microsoft Excel 2007 software packages. Statistical significance was set at P≤0.05. The relative reliability calculations showed significant agreements between repetitions for the mean and peak amplitude and the average of median frequency (MDF) of the studied muscles function during most swallowing types in both groups. However, the duration and particularly the time to peak of muscle activity showed significant agreements during fewer swallowing conditions. Excluding MDF, we found high SEM% and SRD% for the studied measures (particularly timing measures) of muscles function during most swallowing types in both groups. The reliability of sEMG measures was influenced by the age and swallowing types. Our findings suggest that the MDF of muscle function during almost all studied swallowing types can be a reliable measure for the sEMG assessment of swallowing function in both younger and older adults.