Abstract: Since 7α-methyl or 10β-acetoxyestrene-3-ketones were known to show significant anti-implantational or anti-decidual activities, we have synthesized two new steroidal ketones (1_a). and (1_b) possessing both the 7α-or 7β-methyl group and the 10β-acetoxy substitutions according to scheme 1.Experimental animal tests of (1_a) showed that it was effective for termination of early pregnancy on mice with the success rate of 100% (4mg/kg). (1_a) is approximately 3～4 times more potent than (1_b). Results of parmacological tests have been reported elsewhere.