Objective. To detect histological characteristic of anterior cruciate ligament (ACL) and medial collateral ligament (MCL). Methods. In each of 20 skeletally mature male mongrels and 4 men, the ACL and MCL were examined by standard hematoxylin-eosin procedure and toluidine blue staining for histologic observation. Results. The fibroblasts in medial collateral are elongated to spindle shape and aligned in a row between the bundles of collagenous fibers. Toluidine blue staining is negative. The anterior cruciate ligament demonstrated more heterogenous cell types and arrangement. It had three major cell forms:spindle, round and ovoid type, which were shorter but greater than the cells in medial collateral ligament. Toluidine blue staining was positive in anterior cruciate ligament. Most cells in anterior cruciate ligament were enclosed within lacunae. Conclusion. This study suggests that the ACL has different histological characteristics from MCL, and is more cartilage-like in nature.