Planar waveguides in nonlinear optical crystals of Sn₂P ₂S₆ have been produced by He⁺ ion implantation. The effective indices of the waveguide have been determined and refractive index profiles have been evaluated for the indices along all three principal axes of the optical indicatrix. The depth of the induced optical barrier is Δn₁ = -0.07, Δn₂ = -0.07 and Δn ₃ = -0.09 at λ= 0.633μm for a fluence Φ = 0.5 × 10¹⁵ions/cm². Propagation losses for hybrid-n₁ modes are α ≃ 10dB/cm.