The Sony Mobile spec sheet for the Xperia Z says that only microSD memory cards up to 32GB of storage are supported. However, Sony has said that this is the case for most Xperia phones, yet the handsets have always supported larger 64GB cards. Therefore, we were never worried that the Xperia Z will not support 64GB cards and the screenshot below proves this.
The Xperia Z will need to format the 64GB card to FAT32 (from exFAT), but once done you can use the card without any problems. It is worth noting that there is a 4GB single file limit when the card is formatted in FAT32.