We show in this Letter that a double mutant (K51/K39V) of 1prb(7-53), the GA module of an albumin binding domain, has a maximum folding rate constant of similar to1 (mus)(-1). This value is comparable to the estimated theoretical speed limit for protein folding. In addition, we found that the mean hydrophobicity of a given tertiary fold plays an important role in controlling its folding rate.