Abstract: A hydraulic drilling jar for use in association with downhole drilling and adaptable for connection between components of a drill string or the like. The hydraulic drilling jar generally comprises an outer generally hollow hydraulic housing, an inner mandrel assembly, an anvil portion, a hammer portion, and a hydraulic valve. The hydraulic housing has an enclosed first end and an open second end with the first end releasably securable to a first component of the drill string. The mandrel has a first end releasably securable to a second component of the drill string and a second end slidably receivable within the open second end of the hydraulic housing to forming an internal fluid chamber between the mandrel and the housing. The mandrel is also slidable within the outer housing from a contracted position to an extended position. The hydraulic housing and the mandrel operatively connect the first and second components of the drill string.