Set LineJoin for Pen
using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; public class Form1 : Form { protected override void OnPaint(PaintEventArgs e) { Graphics g = e.Graphics; g.SmoothingMode = SmoothingMode.AntiAlias; g.FillRectangle(Brushes.White, this.ClientRectangle); Pen p = new Pen(Color.Black, 10); p.LineJoin = LineJoin.Bevel; e.Graphics.DrawRectangle(p, 20, 20, 60, 60); p.Dispose(); } public static void Main() { Application.Run(new Form1()); } }