The atrio-ventricular valves of the normal heart of 100 Chinese adult cadavers were studied. The right atrio-ventricular (tricuspid) valve was found to be composed of four main cusps in 80% of the cases,three main cusps in 19%,and two main cusps in 1%.In certain cases,small additional intermediate cusps had been found.They were derived from the main cusps and situated in the angles between the medial and anterior wall, or between the medial and posterior wall of the right ventricle.These may be called “cuspi accessoria”.The anterior accessory cusp was present in 31% and the posterior accessory cusp in 27% of our preparations.If the total number of the main and acces- sory cusps of the right a—v valve was considered,four cusps occurred in 42%,five in 36%,three in 13%,six in 8% and two in 1%. The left atrio-ventricular (mitral) valve consisted of two main cusps.But frequent- ly there were conspicuous ruptures on the posterior cusp in our specimens,with the ex- ception of twelve cases (12%).Thus,the posterior cusp may be consisted of one greater leaflet and one to four smaller leaflets.Based on this character,the posterior cusp of the left a—v valve may be grouped into three types:(1)the middle portion of the posterior cusp was well developed in 48%;(2)the antero-lateral portion was well developed in 35%;and (3) the postero-medial portion was well developed in 17%. The anterior cusp of the left a—v valve separated into two equal parts had been found in one case (1%). The height of the cusps and of the commissural margins,where the neighboring cusps were joined,had been measured.Discussions have been made on the principles of the differentiation between the main cusp and the accessory cusp.