Hammett indicator titration was used for the characterization of TS-1 acidity. The acid strength of the TS-1 studied was +3.3 < H0≤ +4.8. The weaker acid sites, +3.85 < H0 ≤ +4.8, were due to the framework Ti of TS-1, while the stronger acid sites, +3.3 < H0 ≤ +3.85, in micron-sized TS-1 samples were due to amorphous extraframework Ti species. The stronger acid sites showed a correlation with the conversion of propylene oxide in the etherification with methanol. The weaker acid sites, although too weak for the etherification of PO with methanol, were active and selective for converting ethyldiamine (EDA) into piperazine (PIP) and 1,4-diazabicyclo[2.2.2]octane (DABCO). TS-1 as a weak solid acid was shown to be a promising catalyst for reactions like the cycloamination of EDA to PIP and DABCO.