Although the laser Thomson scattering has been believed to be the most accurate diagnostic method as a standard of the low temperature plasma metrology, the measurand (electron density and temperature) includes experimental uncertainty and the uncertainty can propagate to the uncertainty of the measurand. Because the uncertainty is induced from the input quantities such as a scattering signal or a stray light signal, analysis of uncertainty of the input quantities and ultimately the measurand is needed. In this paper, uncertainty of the measurand using the laser Thomson scattering method is in detail analyzed in helicon plasmas in which the measurement of plasma parameters is still remained as a challenging issue.