In a previous communication, the structure and absolute configuration of buxtauine and buxpiine, alkaloids extracted from Buxus sempervirens L., were reported; these are steroidal bases of a new type with a single nitrogen atom, a cyclopropane ring, and a keto group in position 20. In the present note, a structure is proposed for a new alkaloid, buxpsiine, isolated by chromatography on alumina from an alkaloid mixture (fraction "C") of B. sempervirens. Buxpsiine has the formula C26H39ON (calculated %: C 81.83, H 10.36, N 3.67; found %: C 81.96, H 10.79, N 3.52), molecular weight 381, melting point 176-178°C, and [α]D +105° (CHCl3, c=0.18). Its UV spectrum has maxima at 240 (log ε 4.73) and 247 nm (log ε 4.62) with a shoulder at 255 nm (log ε 4.43), corresponding to conjugated ketone and conjugated diene chromophores. The ORD curve shows a positive multiple Cotton effect for a conjugated carbonyl group. The IR spectrum displays bands of an α,β-unsaturated ketone at 1612 and 1690 cm⁻¹, with no hydroxyl bands. The NMR spectrum indicates three double bonds (one conjugated with the carbonyl group, the other two forming a conjugated diene). The mass spectrum reveals a molecular ion peak at m/e 381 and peaks (m/e 71, 84, 58, 43, 338, 336, 267) that support the structure. From these results, buxpsiine is determined to have the structure 3β-dimethylamino-4,4',14α-trimethyl-nor-B-homo-pregna-9α(10),9(11),16-trien-20-one. It is a new type of mono-amino steroidal alkaloid belonging to the 19-nor-B-homo series, which also includes diamines like buxamines or buxegines described by Stauffacher and Kupchan.