This dataset gives the viscosity of 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (CAS number: 84030-20-6). The data was measured using a Brookfields rotational viscometer. The sample of 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD) used for the first measurement had a purity of 100.9 ± 1.4 wt%, and the sample used for the second and third measurements had a purity of 97.2 ± 1 wt%.