Background In Japan, four neuraminidase inhibitors (NAIs) are currently prescribed to patients with influenza A and B. To know the backgrounds and clinical courses of patients with influenza who were treated with NAIs is important in the selection of appropriate medications. Methods We conducted a multicenter observational study in Osaka with postcard questionnaires. Patients who were prescribed NAIs were provided postcard questionnaires containing questions on their backgrounds, body temperatures, and durations of other influenza symptoms. We analyzed the factors that were associated with early fever alleviation using a logistic regression model. Results The postcard response rate was 31% (326 of 1050), and 307 patients were enrolled in this study [150 patients who were under 10 years old (type A, 118; and type B, 32) and 157 patients who were 10 or older (type A, 114; and type B, 43)]. In the patients under 10, the multivariate analysis showed that influenza type (Type B vs Type A; Odds Ratio, 0.13; 95% Confidence Interval: 0.04-0.38) was associated with early fever alleviation. However, NAIs were not related to early fever alleviation. Laninamivir tended to contribute more to early fever alleviation compared to oseltamivir in patients under 10 (Odds Ratio, 2.50;$95% Confidence Interval: 0.90-7.80). Conclusions The types,of prescibed NAIs were not significantly related to early fever alleviation. However, the fever durations of the patients under 10 who were prescribed laninamivir were shorter than those of patients under 10 who were prescribed oseltamivir or zanamivir.