As part of our work on the absorption solar refrigeration cycle and with the object to optimize the efficiency of flat plat collector in generation phase, an experimental study has been conducted on the boiling heat transfer of NH3-H2O mixtures flowing inside a 6 mm inner diameter vertical smooth tube. The used experimental device is presented. Using a water-heated double pipe type generator, the local heat transfer coefficients are measured inside the inner tube for a range of heat flux (8.211–18.521 kW/m2 ), mass flux (707–2688 kg/m2 .s), mass flow rate (0.02 –0.076 kg/s), equilibrium mass quality (0–0.6) and ammonia mass concentration (25% - 61%). Three theoretical models are used to predict the boiling heat transfer coefficients. Experimental data were compared with the available correlations. The obtained results confirm the good performance of Bennett-Chen’s correlation in predicting boiling heat transfer coefficient of ammonia water mixtures. This correlation is able to predict the boiling heat transfer data within an accuracy of ± 15 %.