  We have carried out in-plane resistivity measurements under a uniaxial
pressure in NaFe$_{1-x}$Co$_x$As single crystals. A clear distinction of the
in-plane resistivity $\rho_a$ and $\rho_b$ with the uniaxial pressure along
$b$-axis was discovered in the parent and underdoped regime with the doping
level up to about x=0.025$\pm$0.002. From the deviating point of $\rho_a$ and
$\rho_b$, and the unique kinky structure of resistivity together with the
published data we determined the temperatures for the nematic, structural and
antiferromagnetic transitions. It is clearly shown that the nematic electronic
state vanishes simultaneously with the structural transition. The
antiferromagnetic state disappears however at a lower doping level. Our
results, in combination with the data in BaFe$_{2-x}$Co$_x$As$_2$, indicate a
close relationship between nematicity and superconductivity.
