1) Draw the line whose perpendicular bisector has to be constructed.
2) Take a compass, and place it on any of the two end points of the line.
3) With radius more than half of the line, make arcs on either side of the line.
4) Now place the compass on the second end point of the line and with the same radius, cut arcs on the first arc that you made.
5) Draw a line passing through the points where the two arcs intersect o both sides of the original line.
6) The line that you made just now is the perpendicular bisector of the original line.