After extensive studies of the regenerated meniscus, most of authors believe that newly replaced meniscus completely consisted of fibrous connective tissue Instead of forming fibrocartilaginous tissue. This experiment was planned to investigate the chronological effect on the normal menisci and replaced one which formed after meniscectomy In rabbits knees. Total meniscectomy was performed on the medial menlsci of both knee joints of the 40 young rabbits (5 weeks old), weighting from 300 to 400 gm and 40 adult rabbits weighting from 1800 to 2200gm. In both groups, meniscal specimens were obtained from medial area of both knee joints 3,5, 12,24 and 48 weeks following meniscectomy respectively. Medlcal meniscl of normal 5,12,24 and 48 weeks old rabbits were used as control. Each specimen was examined grossly and histologically. Serial histological sections were cut at 6um and stained with hematoxylin and eosin for the histological examination and Safranln-0 fast green Iron hematoxylin for the histochemical examination. The result obtained were as follows: 1. Macroscopically all regenerated meniscl were less shlny and smaller than normal. Its margin was blunt shaped and completely connected with synovial membrane. 2. The meniscus, at 5 weeks after birth was composed with flbroblast and flbrocyte without cartilage cells. At 12 weeks after birth, In 2 out of 4 menisci flbrocytes were transformed with round oval shaped cells with lacunae and they looked Immature cartilage cells and Iightly stained with Safranin-O. 3. In young experimental rabbits, cartilage cells were found in one out of 14 regenerated meniscl at 12 weeks after meniscectomy while in mature rabbits cartilage cells were found in 2 out of 13 regenerated meniscl at 24 weeks after meniscectomy and newly formed 3 menlsci were strongly stained with Safranin-0. Mean rate of cartilage transformation of regenerated meniscl was 10.6% in young rabbits and 8.1% In adult rabbits without much difference in Incidence of transformation rate. Cartilagenous transformation in the small area of regenerated menlscus was found In 10% of cases. It ls summarized from the result that regenerated meniscl firstiy composed with fibrous tissue, but later on regenerated meniscus partiy transforms Into cartllage cells but not entirely. It is speculated that this cartllaginous transformation is due to adaptive metaplasia.