The effect of constant magnetic fields on dislocation anharmonicity of p type silicon single crys tals with a conductivity of 6 Ω cm has been studied. It has been found that preliminary exposure of dislocation silicon (with a dislocation density of 10 4 -10 6 cm -2 ) to a constant magnetic field (B = 0.7 T, t = 30 min) at room temperature causes a change in the nonlinear fourth order elastic modulus β d . The observed changes are associated with the dynamics of magnetosensitive complexes of structural defects and, hence, with the changes in the length of the vibrating dislocation segment. Based on the dynamics of β d (t) after sample expo sure to a magnetic field, the conclusion is made about an increase in the vibrating dislocation segment length L d by 30%, and the characteristic relaxation times of observed effects are estimated.