InAsSb ternary alloys can be considered as an alternative to HgCdTe for mid-wavelength, as well as long-wa-velength infrared applications. Its energy bandgap exhibits nonlinearity versus Sb composition, and hence the correct determination of its value is necessary for the effective design and simulation of optoelectronic devices. The commonly used expression on the InAsSb energy bandgap provided by Wieder and Clawson overestimated energy bandgap values at high temperatures. In this paper, we present two modified empirical relationships which are based on the experimental data obtained in our laboratory and published literature. Both are correct for a wide range of Sb molar composition and temperatures. The nonlinearity of the energy gap is described with the adequate bowing parameter. The data collected in our experiment, for samples grown on lattice mismatched GaAs substrates, fits well with a bowing factor of C=0.72 eV. The minimum bandgap energy that can be reached at room temperature is about 73 meV for a Sb mole fraction, x=0.63. In comparison, the bandgap at low temperatures collected in the literature for samples grown on lattice-matched GaSb substrates is smaller than the measured values in our experiment and fits well with a parabola with C=0.9 eV.