In order to improve the ionic conductivity of lanthanum silicates, which have been considered as the new electrolyte candidates for intermediate temperature solid oxide fuel cells (IT-SOFCs), the feedstock powders are prepared by sintering the mixed oxide powders in different temperatures and sintering times. The main phase of all the samples is the hexagonal apatite structure. The apatite-type ceramic coatings with a typical composition of La10(SiO4)6O3 are deposited by atmospheric plasma spraying (APS). The influence of sintering time of feedstock powders on the electrical properties of La10(SiO4)6O3 electrolyte coatings is reported here. The highest conductivity of the dense composite electrolyte coatings reaches 6.8×10-6 S·cm-1 at 435 °C in air which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.