D. c. electrical conductivity of single crystals of NaClO
3
with varying concentrations of divalent cation impurity are studied. The low-temperature conductivity data are analysed to obtain the association energy between the divalent cation impurity and the cation vacancy. By a suitable analysis developed for the extrinsic and intrinsic overlapping region the formation energy per defect pair has been determined. Almost all the defect parameters are determined by graphical treatment of the conductivity data. Finally these parameters are refined by a least square fit of the conductivity data. The values of the various parameters obtained are: (1) impurity-vacancy association energy E
a
= 0.22 ± 0.01 eV. (2) jump activation energy of cation vacancy E
1j
= 0.46 ± 0.01 eV. (3) pre exponential factor for vacancy mobility
μ
01
= 0.004 cm
2
V
‒1
s
-1
. (4) jump activation energy of interstitial cation E
2j
= 0.85 ± 0.04 eV. (5) pre-exponential factor for interstitial mobility
μ
02
= 14.7 cm
2
V
‒1
s
‒1
. (6) formation energy of a Frenkel defect pair
E
t
= 1.98 ± 0.02 eV. (7) entropy of formation of a Frenkel defect pair
S
t
= 3.0 x 10
‒3
eV K
‒1
.