Purpose Vasculitis is a refractory disease with no established treatment. Therapeutic effect of gamma globulin (IgG) in high dose therapy (IVIg) has been reported (1). IgG preparation which depends on human-derived material, is not completely safety, and supply amount of it is finite. Development of recombinant gamma globulin having the same effect has been requested.<br> Methods We constructed a library of recombinant single chain fragment of variable region (hScFv) of IgG from the constitution of VH-CH1-hinge from peripheral blood lymphocytes of healthy volunteers. One thousand recombinant hScFv clones were analyzed in base sequence, and selected by having the correct structure of hScFv. Selected clones were mixed and cultured, and induced hScFv proteins were administered to spontaneous vasculitis mouse model SCG/Kj to evaluate therapeutic effects.<br>Results From the base sequence analysis of 1,000 clones, we obtained 245 clones having VH-CH1-hinge structure, then a library having 204 clones was established. All 204 clones were mixed and cultured to induce hScFv proteins. A purified preparation was administered into SCG/Kj mice. The hScFv administration at a concentration of 1/20 of the large amount of IgGs preparation showed same effect for suppression of glomerular crescent formation and a refinement of the peripheral blood cell was observed in hScFv administration groups. Also, a biomarker MPO-ANCA titer remarkably decreased at administration dose of IVIg in 1/10.<br>Conclusions The hScFv protein mixture showed therapeutic effects with 1/10 – 1/40 of IVIg in administration to SCG/Kj mouse. It seems to be a development possibility to actual preparation as recombinant IgG.