The slow evaporation technique of an aqueous solution was used to grow single crystal of β-LiNH4SO4 at 309 K. Then, the FullProf program was used to evaluate the structural parameters for this crystal at room temperature (phase II) by two methods (Le Bail and Rietveld). The structural parameters of β-LiNH4SO4 crystal (phase II) obtained by the two methods were compared with each other and with those obtained in some earlier studies, then the agreements and differences were discussed. The crystal structure of β-LiNH4SO4 (phase II) was drew by the FullProf program in accordance with atomic positions, and it was compared with that drew and described previously by other programs. The average crystallite size of β-LiNH4SO4 crystal was calculated by using two equations (Debye–Scherrer and Williamson–Hall), and by using the two methods (Le Bail and Rietveld).