The purpose of this study was to analyze the changes in physicochemical characteristics and NDMA formation of Orostachys japonicus A. Berger according to harvest times. The results showed moisture, carbohydrate, crude fiber and crude protein contents of <$48.5{pm}1.4%$, $38.2{pm}1.2%$, $l5.8{pm}0.4%$ and $13.2{pm}0.6%$ respectively. The total mineral content was 4,817.1 mg/100 g, where Ca was highest($2,577.0{pm}3.2$ mg/100 g), followed by K, Mg, Na, P and Fe. The composition amino acid of O. japonicus A. Berger showed high levels of glutamic acid and aspartic acid. And among the five free sugars detected, galactose and glucose were most abundant at $32.2{pm}0.02$ mg/100 g and $25.3{pm}0.1O$ mg/100 g, respectively. Upon comparing O. japonicus A. Berger extracts that came from plants harvested during $August{sim}October$, total phenolic compound($2,703.l{pm}5.2l{sim}2,428.0{pm}3.52$ mg/100 g) and flavonoid($634.2{pm}2.33{sim}1,324.6{pm}1.87$ mg/100 g) contents were higher in the methanol extract than in the water extract. Also, within a reaction system, nitrite scavenging ability and NDMA inhibition were most effective at pH 2.5, and increased in proportion to the extract concentration. Finally, the methanol extract of O. japonicus A Berger harvested during $August{sim}October$ had the highest nitrite scavenging and NDMA inhibition effects.