We report the effect of chemical composition variation on the superconductivity in noncentrosymmetric β-Mn-type high-entropy alloys (HEAs) studied in two very similar TaMoWReRuC and TaWMoReRuC series. It is found that both HEAs consist of a single cubic β-Mn-type phase for 0 ≤ x ≤ 6 and 0 ≤ y ≤ 9. Bulk fully gapped superconductivity is observed for all these HEAs and their zero-temperature upper critical fields approach the Pauli paramagnetic limit. While our analysis suggests that T of these HEAs is mainly controlled by the electron–phonon coupling strength, T of the TaMoWReRuC series is always higher than that of the TaWMoReRuC one even for (nearly) the same valence electron concentration and unit-cell volume. This difference is attributed to the different contributions of Mo and W to the electronic structure, which is supported by the first-principles calculations. Our study suggests that the chemical composition effect should be considered to better understand the superconducting behavior in noncentrosymmetric HEAs.