The present invention relates to a poly(p-xylylene)-based polymer having a low dielectric constant suitable for low loss dielectrics (LLD), and an insulating material, a printed circuit board and a functional element using the same. More particularly, the poly(p-xylylene)-based polymer includes at least one repeat unit expressed by the following formula (1): wherein, at least one of R1, R2, R7 and R8 is independently substituted or unsubstituted C6-C20 aryl; the rest of R1 to R8 are each and independently H, substituted or unsubstituted linear C1-C3 alkyl, or substituted or unsubstituted branched C1-C3 alkyl; and n is an integer of 400 to 900.