We make a mathematical analysis of an age structured HIV infection model with both virus-to-cell and cell-to-cell transmissions to understand the dynamical behavior of HIV infection in vivo. In the model, we consider the proliferation of uninfected CD4 + T cells by a logistic function and the infected CD4 + T cells are assumed to have an infection-age structure. Our main results concern the Hopf bifurcation of the model by using the theory of integrated semigroup and the Hopf bifurcation theory for semilinear equations with nondense domain. Bifurcation analysis indicates that there exist some parameter values such that this HIV infection model has a non-trivial periodic solution which bifurcates from the positive equilibrium. The numerical simulations are also carried out. .cn (Z. Liu).where T , I and V denote the population of uninfected CD4 + T cells, productively infected CD4 + T cells and virus, respectively. They treated the logistic proliferation term rT 1 − T +I K in which r is the maximum proliferation rate and K is the uninfected CD4 + T cells population density at which proliferation shuts off. Since the proportion of productively infected CD4 + T cells I is very small and thus it is reasonable to ignore this correction. They eventually represented the proliferation of uninfected CD4 + T cells by a logistic function rT 1 − T K . However, the authors only consider the classical virus-to-cell infection and neglect the direct cell-to-cell transmission.[12] incorporated the two modes (virus-to-cell infection and cell-to-cell transmission) of transmission into a classic model and considered the following model system+∞ 0 q(a)i(t, a)da, ∂i(t,a) ∂t + ∂i(t,a) ∂a = −σ(a)i(t, a), dV (t) dt = ∞ 0 p(a)i(t, a)da − cV (t),