Late embryogenesis abundant (LEA) proteins are synthesized during the late stages of seed development and have been widely reported in monocot and dicot plants. We have selected several cDNA clones of seed maturation proteins from a soybean pod-dried seed cDNA library by differential screening and these clones are designated GmPM clones, which stands for Glycine max physiological mature. In the present study, we study the characteristics and developmental regulation of a soybean gene family encoding GmPM1 and GmPM9, two typical type IV LEA proteins. Sequence alignment of the GmPM1/9 proteins with other similar proteins found in the database indicates extensive similarity at the N-terminus. The β-glucuronidase (GUS) reporter gene driven by the GmPM9 promoter was induced at significant levels in late developing seeds of the transgenic tobacco plants. Histochemical analysis of GUS activity revealed that the GmPM9 promoter functions in the mature seeds and pollen. To analyze the mechanism of GmPM9 regulation, the truncated promoter was introduced by bombardment into embryonic axis excised from maturing soybean seeds. With only 114 bp of promoter sequence, the GUS expression was stimulated by seed maturity.