Synthesis of the new prostaglandin (PG) analogs sensitive to acid, 16-methylene-PGF2α methyl ester, 16-methylene-PGE2 methyl ester, 16,16-ethano-PGF2α methyl ester, and 16,16-ethano-PGE2 methyl ester, is reported. These PG analogs have higher biological activities but have fewer side-effects.