The impact of the Mt. Pinatubo eruptions on the total column ozone measured from the Nimbus 7 TOMS and the NOAA-11 SBUV/2 spectrometers has been studied. The ozone anomalies inferred from the two instruments agree within 1--2% in the presence of large volcanic clouds produced by Pinatubo. The Pinatubo eruptions took place on June 15--16, 1991 during the easterly phase of the quasi biennial oscillations (QBO) and as such present a different dynamical scenario for the changes in statospheric ozone compared to the El Chichon eruptions which took place during the westerly phase of the QBO. Within a few months after the eruptions, the total column ozone decreased by 5--6% in the tropics, 3 to 4% at mid-latitudes and 6--9% at high latitudes in the northern hemisphere. However, after the effects of QBO and interannual variability are taken into account, the decrease in the column ozone attributed to volcanic eruptions at these latitudes may not be more than 2--4%-a conclusion in general agreement with a similar study of the El Chichon effects on the stratospheric ozone. The most noticeable effect of the Pinatubo eruptions, as observed during the El Chichon period, is the breakdown of the phase relation between ozone and temperature. This is attributed to additional heating in the lower stratosphere caused by volcanic aerosols.