Gridlines are the horizontal and vertical lines that appear on a chart to help you align data points. By default, Microsoft Excel displays gridlines on a worksheet when you view it in Normal view. You can control whether gridlines appear on a chart by making changes to the chart's Gridlines property.
To access the Gridlines property, select the chart, and then click the Format tab. In the Current Selection group, click Selection Pane. This displays a list of all the objects on the worksheet, including the chart and its associated elements.
In the list of objects, click Gridlines, and then click Format Selection. This displays the Format Gridlines dialog box.