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The effect of an osmoticum, polyethylene glycol (PEG), on somatic embryo production was examined using embryogenic cells of Pinus densiflora. In the basal medium containing 30 µM abscisic acid and 6% maltose, the quality of the embryos formed was poor even though somatic embryos were produced. The addition of PEG with molecular weight of 4000 or 8000 significantly enhanced the development of both the quality and quantity of somatic embryos. Furthermore, higher levels of a constant osmotic pressure with PEG 8000 in a range from about 300 to 450 mmol/kg could remarkably enhance the morphogenesis of somatic embryos and their number of embryos produced. A higher stable osmotic pressure with an appropriate molecular weight of PEG is a key factor for the production of good quality somatic embryos in P. densiflora.