Go to Format Cells - Custom. Type the required format into the list first. To prefix "0" before the text characters in an Excel column, use the Format 0####. Remember, use the character "#" equal to the maximum number of digits in a cell of that column. For e.g., if there are 4 cells in a column with the entries - 123, 333, 5665, 7 - use the formula 0####. Reason - A single # refers to reference of just one digit.