How to Get Slimeballs in Minecraft

Guide Java Bedrock

Quick answer: Kill small slimes: each drops 0-2 slimeballs (up to 5 with Looting III). Slimes spawn in swamps and mangrove swamps at night (best on a full moon) or deep underground in slime chunks below Y=40. You can also buy them from wandering traders, get them from sneezing baby pandas, or uncraft a slime block into 9.

What you need

A sword (Looting III ideal)
A swamp at night or a slime chunk below Y=40
Optional: frogs for passive farming
Optional: 4 emeralds for the wandering trader

Step by step

Hunt swamps at night: slimes spawn in swamps and mangrove swamps between Y=51 and Y=69 at light level 7 or less. They spawn most often on a full moon and never on a new moon.
Or dig into a slime chunk: about 1 in 10 chunks is a slime chunk, where slimes spawn below Y=40 regardless of light. In Java the chunks depend on the world seed; in Bedrock they're at the same coordinates in every world.
Split them down: big and medium slimes don't drop anything - they split. Only the smallest slimes drop 0-2 slimeballs, and Looting adds 0-1 per level (up to 5 with Looting III).
Let frogs help: frogs eat small slimes whole and each one drops 1 slimeball - a frog pen in a swamp is an easy passive farm.
Watch baby pandas: a sneezing baby panda has a 1/700 chance to drop a slimeball. Slow, but free if you keep pandas.
Buy or uncraft: wandering traders sell 1 slimeball for 4 emeralds, and a slime block crafts back into 9 slimeballs - handy if you have blocks but need balls.
Spend them on: sticky pistons, slime blocks, magma cream, frog breeding -, and breeding frogs (they also shorten tadpole growth by 10%).

Java vs Bedrock

Two Bedrock differences: slime chunks sit at the same coordinates in every world (Java chunks depend on the seed), and killing a wandering trader who is offering slimeballs while you hold an emerald has an 8.5% chance (+1% per Looting level) to drop one.

Versions: Slime size is affected by regional difficulty: from 33% for each size at low difficulty to 16% small, 33% medium and 50% big at higher difficulty.

Frequently asked questions

Where do slimes spawn?

Two places: swamps and mangrove swamps at night between Y=51 and Y=69 (a full moon is best), and slime chunks below Y=40 where light doesn't matter. About 10% of chunks are slime chunks.

Why aren't slimes dropping slimeballs?

Only the smallest slimes drop slimeballs (0-2 each). Big and medium slimes split into smaller ones when killed - keep fighting until you finish the smallest size.

Can you farm slimeballs without slimes?

Yes: frogs eat small slimes and drop 1 slimeball each, baby pandas sneeze them out (1/700 chance), wandering traders sell them for 4 emeralds, and slime blocks uncraft into 9.

What are slimeballs used for?

Sticky pistons, slime blocks and magma cream, and breeding frogs.