Duplex (Double-Sided) Printing in Mac

While installing your printer, you must selected the printer model from the Print Using drop down box! (The printer model must NOT be Generic PostScript Printer) If you did not set it up right, you need to delete the printer and set it up again.

1. Go to the System Preferences and click Print & Fax.
2. Click on the printer you want to change and then click on Printer Options.
3. Select Installable Options from the drop down menu.
4. Check duplex unit.

When printing

From the print options box select Layout dropdown menu and then select Long Edge Duplex