Abstract: In this paper, the semiparametric generalized partially linear models (GPLMs) for longitudinal data is studied. We approximate the nonparametric function in the GPLMs by a regression spline, and use quadratic inference functions (QIF) to take the within-cluster correlation into account without involving direct estimation of nuisance parameters in the correlation matrix. We establish the asymptotic normality of the resulting estimators. The finite sample performance of the proposed methods is evaluated through simulation studies and a real data analysis.