Why is my SD card read-only on Android?

Last reviewed: October 29, 2026 · Markdown version

Start with one test, because "read-only" covers two different situations. Open your phone's own file manager (Files by Google or Samsung My Files), and try to copy a small photo onto the card. If that fails too, the card or its format is the problem. If it works, the card is fine and it is one app that cannot write there, which is a permission question, not a fault.

Read-only for every app

Android has a name for this state. Its developer guide tells apps to check the storage state, and says that if it is "MEDIA_MOUNTED_READ_ONLY, you can only read these files" (Access app-specific files, Android Developers, read 29 October 2026). That page does not list the reasons a card ends up mounted that way; on causes it is silent. The candidates the vendors do document:

A file system the phone does not fully support. Samsung: "the file system must be FAT32 or exFAT (preferred)", and "NTFS (common on Windows PCs) and APFS (common on Macs) are not compatible" (MicroSD cards and your Galaxy phone or tablet, Samsung US, read 29 October 2026). A card last formatted on a computer is the usual suspect.
The adapter's lock. A microSD card has no switch, but a full-size adapter does: the SD Association's comparison table lists a "Write-protect Switch" as yes for full-size cards and no for microSD (SD Standard Overview, SD Association, read 29 October 2026), and its formatter FAQ says the position "should be in NOT PROTECTED mode (i.e., positioned upward)" (FAQ, SD Association, read 29 October 2026). This matters when the card has been through a computer, not inside the phone.
A card that is failing. Samsung's troubleshooting page says "A malfunctioning SD card can cause data loss and device performance issues. It should be replaced or removed" (Issues with SD cards on Samsung phone or tablet, Samsung US, read 29 October 2026). In our experience a card that suddenly refuses writes after years of use is often wearing out, and the first job is to copy everything off it.

Fixing the first and third usually means formatting, which erases the card, so copy the files to a computer first. The steps, and what to do when formatting fails, are on our formatting page and the corrupted-card page.

Read-only for one app

Since Android 10, apps no longer get free run of shared storage. Google's guide says "apps that target Android 10 (API level 29) and higher are given scoped access into external storage, or scoped storage, by default" (the Access app-specific files page above). The same page says an app "doesn't need to request any storage-related permissions to access app-specific directories within external storage", which on a phone with a card can include the app's own folder on it. Writing anywhere else on the card is where the limits bite. The broadest route Google describes is "all-files access", which a user grants on a settings page labelled "Allow access to manage all files", and which includes "Access to the root directory of both the USB on-the-go (OTG) drive and the SD card" (Manage all files on a storage device, Android Developers, read 29 October 2026). So an older app, or a camera or download app that was never given a folder on the card, will see it as read-only while your file manager writes to it happily. The fix is in that app: pick the card again as its save location, or grant the access it asks for. More on scoped storage.

A quick decision list

File manager can write, one app cannot: the app's permission or save setting.
Nothing can write, and the card came from a computer: check its file system, then format it in the phone after copying it off.
Nothing can write, and the card has been in this phone for years: back it up now and plan to replace it.