AbstractThe use of a two mole percent n‐butane in helium stream in a fixed bed mini‐reactor at a temperature of 500°C over a zeolite bed (20 to 40 mesh and ≤ 5 grams in weight) was found to be a good tool for characterizing zeolitic acidity. In a broad spectrum of various kinds of zeolites tested, the test results are especially useful in differentiating the extremely active materials from the very active ones. Among the zeolites tested, the decreases in the order of HΩ>H‐Zeolon>NH4‐ZSM‐5>NH4Y (thermally modified)>NH4‐erionite (thermally modified)>>HKL>NH4Y>NaY ˜ amorphous silica‐alumina. The calculated first order rate constant covered a range from over 10