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Methods of growing Si whiskers are considered and the results of studying their magnetic susceptibility χ are reported. Silicon whiskers are grown using the method of chemical transport reactions in a closed bromide system. The crystals studied were divided into four groups: (i) crystals 0.1–0.9 μm in diameter, (ii) twinned crystals 1–2 μm in diameter, (iii) needle-like crystals from 5 to 1500 μm in diameter, and (iv) isometric crystals (the latter were not measured). With an increase in diameter, the whiskers of the first group changed their state from paramagnetic to diamagnetic, while the crystals of the third group showed a transition from a diamagnetic to a paramagnetic state. All these crystals show a nonlinear dependence of χ on the strength of an external magnetic field H; the nonlinearity increases with increasing the sample paramagnetism. The susceptibility of twinned samples is diamagnetic and close to the value of χ for bulk silicon, and the nonlinearity of the dependence χ (H) is insignificant. The measured values of χ of Si whiskers are explained by features of their crystal structure and chemical composition.