Objective: To discuss the significance of IgG4 in the pathogenesis of connective tissue disease with interstitial lung disease and its relationship with activity of the disease.Method: There were 205 cases of patients with connective tissue diseases, who were randomly divided into two groups.Among them, there are 93 cases with interstitial lung disease, but 112 cases without interstitial lung disease.Serum IgG4 levels of all patients were detected by immune nephelometry quantitative method, and IgG4 level changes between the two groups were compared.At the same time, the levels of ESR, CRP, IgA, IgG and IgM were detected in 93 patients with interstitial lung disease, also the correlation of the activity and IgG4 were analyzed.Results 1.Compared with serum IgG4 levels in group of connective tissue disease with interstitial lung disease patients and the group without interstitial lung disease ,there were no significant difference (P > 0.05);2 Serum IgG4 levels in patients with interstitial lung disease secondary to connective tissue disease and levels of ESR, CRP, IgM, IgA and IgG have no significant correlations (P > 0.05).Conclusion There were no correlation with IgG4 and connective tissue disease with interstitial lung disease, suggesting that IgG4-related diseases and connective tissue disease are two independent immune system disease.And serum IgG4 level cannot be used as judgment of activity in connective tissue disease with interstitial lung disease.