Try some WD-40 or lubricating oil for machines on the bearings. Make sure the fan is off and let it work for a few minutes before turning the fan back on. If it solved most of the problem, try just a little more WD-40. In many cases, this will solve the squeaky problem.
Tighten any screws or bolts. Perhaps two loose pieces rubbing up against each other is causing the squeaking.
Clean your fan and get rid of any dust in the bearings. You can use a can of compressed air to get all the dust out.
Make sure the fan is balanced. If it's wobbling and that's causing the squeaking, you've got a bigger problem on your hands than just a squeaking ceiling fan. Try balancing the weights (with a balancing kit purchased at a home improvement store) or changing the fan blades to fix the wobbling.
Consider replacing the ceiling fan. Sometimes squeaking is just the first symptom of the bad bearings.
- Always turn off your fan before playing with it or attempting to fix it.