We report the first (to our knowledge) experimental observation of passive synchronization between a 1.03 μm. self-similar pulse and a 1.56 μm. bound-soliton bunch in a two-color mode-locked fiber laser. The self-similar pulse can form an effective potential well of several picoseconds to trap the copropagating bound solitons in the shared-fiber section. Such synchronization mechanism is supported by the experimental evidence of smaller time separation between the bound solitons under synchronization. In addition, the selfsimilar pulse and bound solitons can still remain locked under the periodic collision of another 1.56 μm unlocked pulse train.