[Summary] This paper reported a case of 4-year-old boy suffered with medial meniscus tear treated by arthroscopic repair in our hospital.After the boy injured his knee , plaster was applied for 4 weeks.Without any symptomatic progress , he was hospitalized with the diagnosis of medial meniscus tear .We performed arthroscopic meniscus repair , using 4.0-mm arthroscopy.At 3-month follow-up, the boy could full-bearing walk with no pain or discomfort , with a range of motion of 0°-135°.The post-operational MRI at the fourth month showed preliminary healing of repaired meniscus .We believe that regular arthroscopic instruments can accomplish meniscus repair in young children .