Objective To study the related factors of intradiscal injection of collagenase. Methods One hundred and sixty eight patients with lumbar disc herniation were injected with collagenase(600U) under X ray monitoring. Assessment of efficacy of the treatment was made in 1 week, 3 months and 1 year follow up. The parameters such as the size, the type and the number of herniated disc were studied. The effect of stenosis was also analyzed. Results The overall success rate after 1 week, 3 months and 1 year following the therapy was 22.62%, 89.29% and 92.26% , respectively. Seven patients were treated with surgical operation during the follow up, 1 developed cauda equina syndromes at the third day after the injection. It was found that the size of herniation did not affect the efficacy of the treatment. The protruded disc got better result than bulge disc after 1 week following the chemonucleolysis ( P