Abstract: Embryogenic suspensor mass (ESM) of slash pine was induced with the non-mature zygotic embryos as explants. The maintenance,proliferation and maturation of ESM culture were studied with medium optimization. The results indicated that (a) the basic medium in combination of plant growth regulation (PGR) agents affected the proliferation rate and the quality of somatic embryos (SEs); (b) the optimized medium contained DCR+1.0 mg NAAL-1+0.32 mg 6-BAL-1+0.30 mg KTL-1; (c) in medium without PGR,the pretreatment was necessary for the development and maturation of SEs of the slash pine; (d) the combination of ABA,PEG,AC and a high concentration of sucrose improved the maturation of SEs; and (e) the SEs developed into stage 5 on medium of LP+50 mg ABAL-1+20% PEG6000+6% sucrose+2.5 g ACL-1,but no mature embryo was obtained.