Seed development and vigor may be influenced by harvest time and height of harvest in onion seeds.Thus,an experiment was conducted to evaluate the effects of different harvest times and height of harvest in enzymatic activity and biochemical changes of seeds in two growth seasons(2014-2015) at Research Farm of the Seed and Plant Institute,Karaj,Iran.The experimental design was a factorial in a randomized complete block with three replications. Four times of harvest (T1(moisture content:60%), T2(moisture content:50%), T3(moisture content:39%), and T4(moisture content:11%)) and four harvest height (0,10,20and30cm bottom of inflorescence) were randomized to the plots. Seeds were harvested in 10 days intervals at four stages during development and maturity. The results showed in both of studied years the maximum catalase(1.847 OD/mg protein min-1) and peroxidase activity(3.852 OD/mg protein min-1) and also the minimum MDA content(0.068 nm g FW) were achieved in 3rd harvest time and 20cm height of harvest. In agreement with the achieved result about enzymatic activity, the maximum 1000seed weigh (4.440g) was observed in the second year and third harvest with 20cm height of harvest. Maximum seed vigor as measured by the electrical conductivity of seed leachate(58.70 μs/cm/g) was obtained at second harvest time with 20cm height of harvest. In this study, earlier harvests due to immaturity and later harvests because of aging reduced seed vigor of onion. The best treatment for achieving suitable seeds was third harvest time and 20cm height of harvest.Also, biochemical traits were helpful in determining the suitable time of harvesting in onion seeds. Manuscript profile