The unclamped electro‐optic coefficients were measured in ferroelectric NaNO2. The following values were obtained at 150°C, in units of 10−10cm/V:ra=r22− (n3/n2)3r32= 4.1;rb=r32− (n1/n3)3r12= 4.2;rc=r22− (n1/n2)3r12= 0.6;r43= − 1.9;r61= − 3.0. The constantsraandrcvary approximately as &egr;2does near the Curie temperature, as expected, butrbdoes not, decreasing toward zero atTc. No significant temperature dependence was found inr61orr43. The quantityrachanges sign as a function of temperature at 115°C. The observed behavior can be explained in terms of a temperature‐independent response including both second‐ and fourth‐order terms, biased by the spontaneous polarization.