We are interested in the problem of reconstructing sound soft acoustic obstacles using multifrequency far-field measurements. This problem has two common difficulties: Ill-posedness and limited resolution (diffraction limit). On the one hand, at low frequencies, we know that the reconstruction problem is uniquely solvable, see [1], but its stability is poor. That means, at low frequencies, it is difficult to reconstruct small details of the obstacle. On the other hand, at high frequencies, this inverse problem may not be uniquely solvable but it is more stable [2]. To take the advantages of both low and high frequencies, we design an MCMC method using multifrequency data. [1] Colton, D., & Sleeman, B. D. (1983). Uniqueness theorems for the inverse problem of acoustic scattering. IMA journal of applied mathematics, 31(3), 253-259. [2] Sini, M., Thanh, N. T., & Rundell, W. (2012). INVERSE ACOUSTIC OBSTACLE SCATTERING PROBLEMS USING MULTIFREQUENCY MEASUREMENTS. Inverse Problems & Imaging, 6(4).