To gain insight on the mass assembly and place constraints on the star formation history (SFH) of Lyman break galaxies (LBGS), it is important to accurately determine their properties. We estimate how nebular emission and different SFHs affect parameter estimation of LBGs. We present a homogeneous, detailed analysis of the spectral energy distribution (SED) of similar4700 LBGs from the GOODS-MUSIC catalogue with deep multi-wavelength photometry from the U band to 8pm to determine stellar mass, age, dust attenuation, and star formation rate. Using our SED fitting tool, which takes into account nebular emission, we explore a wide parameter space. We also explore a set of different star formation histories. The physical parameters of approximately two thirds of high redshift galaxies are significantly modified when we account for nebular emission. The SED models, which include nebular emission shed new light on the properties of LBGs with numerous important implications.