The activity of restriction enzymes are affected by the following factors: 

Temperature - Most restriction enzymes work most efficiently at 37°C, but there are a few exceptions. Some work best at higher temperatures ranging from 50°C to 65°C, while a few cut best at lower temperatures of about 25°C.

Buffer systems - Most restriction enzymes exhibit maximum activity in the pH range of 7.0–8.0. 

Ionic Conditions - Most restriction enzymes need Mg2+ but a few also require ions such as Na+ and K+.

Cofactors - Most restriction enzymes need certain cofactors or combinations of cofactors to facilitate digestion at the recognition site. All enzymes require Mg2+ as a cofactor for the endonuclease activity. 

Methylation status of DNA - DNA digestion may be affected by the methylation of adenine or cytidine residues.