An 18-month-old boy suffering from pain and swelling of the right leg and fever, all of which developed　following chickenpox infection, was referred to our hospital. His peripheral blood white blood cell count and CRP were elevated to 19,630 /μl and
9.87 mg/dl, respectively. Streptococcal antigen was detected on the throat swab. T2-weighted magnetic resonance images demonstrated high intensity signal in the fascia on his right leg, suggesting a diagnosis of necrotizing fasciitis（NF）. Upon exploratory incision, surgical debridement and fasciotomy were performed on his leg. After surgery, pain and swelling of the leg and fever disappeared swiftly following antibiotics infusion. Two months postoperatively, he could walk without any impediment. Although NF is generally characterized by rapidly spreading necrosis and a high mortality rate, early diagnosis of NF with MRI followed by timely surgical intervention led to quick recovery of our patient without any major complications.