In order to investigate the effect of different phosphorus and radiation treatments on Azolla growth and water use efficiency (WUE), an experiment was carried out at the Agricultural Research Greenhouse of Razi University, Kermanshah, Iran. The experiment was a factorial with three factors based on a completely randomized design with three replications. The first factor was cultivation dates (4 May and 4 June), the second was radiation levels (0, 50 and 100% of Full sunlight) and the third was phosphorus treatments including control (without fertilizer), chemical fertilizer and chicken manure. Results indicated that the highest dry matter produced and water use efficiency occurred at the 100% level of Full sunlight. At the higher radiation levels (50 and 100% of Full sunlight) chicken manure performed better as compared with the other phosphorus treatments. Moreover, at the 100% of Full sunlight, there was no significant difference between the two cultivation dates in terms of WUE.