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The hyperfine structure of linear triatomic molecules with the Renner effect in $\Pi$ electronic states has been studied, Energy splittings for both Hund’ s case (a) and case (b) have been derived to second order. The zeroth order wave function used here is diagonal with respect to both the vibronic and the spin-orbit interactions. The electron spin-spin interaction is considered as an additional perturbation for splittings of fine structure levels J. Each J level is further split by hyperfine interaction. These results have been applied to the case of NCO $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ states. A comparison of experimental data and calculated values will be given.