The coin had an elliptical shape that resembled koban (former Japanese oval coin), having a square hole in the center, of which Chinese characters '天保通寳' (Tenpo-tsuho) was written on the front, '當百' (Tohyaku; referring that 1 Tenpo-tsuho was equivalent to 100 mon [a unit of currency]) and Kao (written seal mark) of the Goto family, kin-za (an organization in charge of casting and appraising of gold during the Edo period) on the back.
形状は、小判を意識した楕円形で、中心部に正方形の穴が開けられ、表面には「天保通寳」、裏面には「當百」と表記され、金座後藤家の花押が鋳込まれている。