Dispersion of latent-image specks formed by β-radiation was studied for sulfur-sensitized emulsions by means of the arrested development technique. The number of latent-image specks in one grain, n, was counted and the distribution of n was measured. The distribution is wider than that for grains exposed to light and split into two peaks at stronger sensitization levels. One was a broad peak at n ≥ 1 and the other was a sharp peak at n = 0. The average number of β-particles that strike one grain w, was evaluated statistically. The average number of latent-image specks in one grain v,increased with w. The relationship between w and v was linear at small w. It deviated upward for strongly sensitized emulsions and downward for weakly sensitized and unsensitized emulsions. The average number of latentimagespecks formed by one strike of a β-particle, z, was evaluated and it increased with the sensitization level. This value z is useful as a quantitative index of the dispersion of latent-image specks.