  In this work we consider the initial value problem for the generalized
Benjamin equation
  \begin{equation}\label{Benj-IVP} \begin{cases} \partial_t u-l\mathcal{H}
\partial_x^2u-\partial_x^3u+u^p\partial_xu = 0, \quad x,\; t\in
\mathbb{R};\;\;,\; p\geq 1, \\ u(x,0) = u_0(x), \end{cases} \end{equation}
where $u=u(x,t)$ is a real valued function, $0<l<1$ and $\mathcal{H}$ is the
Hilbert transform. This model was introduced by T. B. Benjamin (J. Fluid Mech.
245 (1992) 401--411) and describes unidirectional propagation of long waves in
a two-fluid system where the lower fluid with greater density is infinitely
deep and the interface is subject to capillarity.
  We prove that the local solution to the IVP associated with the generalized
Benjamin equation for given data in the spaces of functions analytic on a strip
around the real axis continue to be analytic without shrinking the width of the
strip in time. We also study the evolution in time of the radius of spatial
analyticity and show that it can decrease as the time advances. Finally, we
present an algebraic lower bound on the possible rate of decrease in time of
the uniform radius of spatial analyticity.
