An oil guiding device for hydraulic brake lever assembly having a brake lever includes a seat connected to the brake lever. The seat has an oil reservoir disposed thereon. The oil reservoir has an oil chamber defined therein. An oil guiding base is disposed in the oil chamber. The oil guiding base has an oil inlet and an oil outlet defined therein. An oil guiding unit engages with the oil guiding base. The oil guiding unit has a pipe disposed thereon and an oil hole defined therein. The pipe and the oil hole are communicated with the oil outlet and the oil inlet respectively. A cover panel engages with the oil reservoir. The pipe sucks up the hydraulic oil gathered in the oil chamber and supplies the hydraulic oil through the oil outlet; the returned hydraulic oil flows into the oil chamber through the oil inlet.