Activity and stability of kiwifruit actinidine was determined in various conditions of pH, salt, and temperature using N-${alpha}$-CBZ-lysine P-nitrophenyl ester as the substrate. Actinidine activity was low below pH 6, and undetectable below pH 3. The enzyme was stable in a pH range of 6.0-8.5. At $4^{circ}C$ the enzyme was inactive in the presence of greater than 36% vinegar and in 2 M NaCl. Actinidine at $25^{circ}C$ was unstable in 24% vinegar but stable in up to 3 M NaCl. With regard to freeze-thaw stability, actinidine retained 85% residual activity after being frozen at $-20^{circ}C$ for 3 days. Based on Arrenius and Lineweaver-Burk plots, actinidine became unstable at greater than $45^{circ}C$ with only 30% residual activity remaining after 6 min. The Km, kcat, and kcat/Km values of actinidine were $56;{mu}M$, 67/sec, and $1.2;{mu}M/sec$, respectively.