A post driver has a housing of tubular form extending substantially vertically, and weight telescopically mounted within the housing for movement between an extended position raised above the housing and a lowered position. A strike pad projects from the weight to drive a post into a hole drilled in the ground. A fluid cylinder mounted within the housing extends from a lower part of the housing to the interior of the weight and is operable to raise the weight to its extended position whereby the weight can then fall to a lower position at which its strike pad engages the upper end of the post.