Every so often, this same "pearl bracelet" queston comes up.
1) Draw a circle (one of the pearls).
2) Drag it to the Brushes Palette. In the resulting dialog, choose New Pattern Brush. In the Pattern Brush Options dialog, select the radio button for Approximate Path. Make sure the Scale is 100% and Spacing is set to 0. Click OK.
3) Draw a circle (the string of the bracelet). Leave it selected.
4) Click on the Brush you just created in the Brushes Palette to apply it to the path.
5) To adjust the number/size of pearls, DoubleClick the Brush attribute in the Appearance Palette and change the Scaling factor.