STEP 1. First you have insert SD card in to the SD slot of memory card reader, then Plug your memory card reader into a USB port on your Mac OS X.
STEP 2. Now you have to open the Finder window. In the Side Bar, click on Applications and scroll down until you find the Utilities folder.
STEP 3. Within Utilities folder, you have to launch Disk Utility application by simply double clicking on it.
STEP 4. In the left-hand Drives column, click on SD card. Now from the top row of radio buttons, click on “Erase” button. Now you have to choose the format you would like to use to format the SD card on the “Volume Format” pop-up button. If you want to use the SD Card on Mac then select Mac OS Extended (Journaled). If you want to share the SD card with both Macs and digital cameras or PCs then select MS-DOS (FAT). After that you have to click on Erase button.
STEP 5. Now you will be able to see a dialogue box in “Disk Utility,” which will ask you to make sure you wish to erase the SD card. Then you have to click on Erase button.
That’s it. Then the SD card will mount on your Mac desktop after it has been erased. You have successfully formatted an SD Card on your Mac OS X. If you found any difficulty in following the above steps then feel free to ask in the comment section below.