For example you have a data range as below screenshot shown, and after adding a chart in Excel, you can format a certain axis and change all axis labels to percentage easily as below:

1. Select the source data, and then create a chart with clicking the Insert Scatter (X, Y) and Bubble Chart (or Scatter) > Scatter with Smooth lines on the Insert tab.

2. In the new chart, right click the axis where you want to show labels as percentages, and select Format Axis from the right-clicking menu.

3. Do one of below processes based on your Microsoft Excel version:
(1) In Excel 2013's Format Axis pane, expand the Number group on the Axis Options tab, click the Category box and select Percentage from the drop down list, and then in the Decimal Places box type 0.
(2) In Excel 2007 and 2010's Format Axis dialog box, click Number in left bar, click to highlight the Percentage in the Category box, and then type 0 into the Decimal places box.

4. Close the Format Axis pane or Format Axis dialog box. Then you will see all labels in selected axis are changed to percentages in the chart as below screen shot shown:

Easily create a stacked column chart with percentage data labels and subtotal labels in Excel

It's easy to create a stacked column chart in Excel. However, it will be a little tedious to add percentage data labels for all data points and the subtotal labels for every set of series values. Here, with Kutools for Excel's Stacked Column Chart with Percentage feature, you can easily get it done in 10 seconds.