We constrain holographic dark energy (HDE with time varying gravitational coupling constant in the framework of the modified Friedmann equations using cos- mological data from type Ia supernovae, baryon acous- tic oscillations, cosmic microwave background radiation and X-ray gas mass fraction. Applying a Markov Chain Monte Carlo (MCMC) simulation, we obtain the best fit values of the model and cosmological parameters within 1σ confidence level (CL) in a flat universe as: Ωbh2 = 0.0222+0.0018 −0.0013, Ωch2 = 0.1121+0.0110 −0.0079, αG ≡ ˙ G/(HG) = 0.1647+0.3547 −0.2971 and the HDE constant c = 0.9322+0.4569 −0.5447.Us- ing the best fit values, the equation of state of the dark com- ponent at the present time wd0 at 1σ CL can cross the phan- tom boundary w =−1.
