Background:  In this study a series of basic dosimetric properties of a low-density (LD) gel dosimeter are investigated. The dose response is studied regarding to linearity, sensitivity, dose-rate and energy dependence as well as lung tissue equivalence. Materials and Methods: The LD gel was made by mixing the polymer gel with expanded polystyrene spheres. Energy dependence was studied at two different energies: 1.25 MeV and 6 MV photon beams which were produced by ⁶⁰Co and Linac machines. Investigation of dose rate dependence was performed in the low, medium, and high absorbed dose regions. Also reproducibility of dose response was studied in three sets of LD gel with identical preparation, irradiation and imaging procedure at three different days. Moreover the linearity and sensitivity were investigated up to 30Gy. Results: The results showed that the dose response was reproducible. The gel response was found linear up to 22Gy with r²=0.981 and sensitivity of 0.814S^-1Gy^-1. In the measured ranges, the dose response of LD gel was independent of beam energy within less than ±0.02 and dose rate had no effect on the gel response. LD gel was nearly lung tissue equivalent with mass density 0.37 to 0.4g/cm3 and relative electron density 0.41. Conclusion: MAGAT LD gel dosimeter appears to be a promising dosimeter in all aspects of dosimetric properties evaluated in this study. In addition, its high linearity together with no dose rate dependence in different level of absorbed doses makes it a suitable dosimeter to measure 3D-dose distributions inside a non-homogeneous media.