We constrain holographic dark energy (HDE) with time varying gravitational coupling constant in the framework of the modified Friedmann equations using cosmological data from type Ia supernovae, baryon acoustic 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 1 σ confidence level (CL) in a flat universe as: {Mathematical expression}, {Mathematical expression}, {Mathematical expression} and the HDE constant {Mathematical expression}. Using the best fit values, the equation of state of the dark component at the present time wd0 at 1 σ CL can cross the phantom boundary w=-1. © 2013 Springer Science+Business Media Dordrecht.