This study evaluated the drying behaviors of complete and compressed water hyacinth (WH) by Multi-tray solar dryer under Kafrelsheikh governorate weather conditions during summer season, 2013. A multi-tray solar dryer, which manufactured and tested in Rice Mechanization Center, Agric. Eng. Res. Inst. for drying fish successfully, was used. Heated air in solar air collector was forced through the drying chamber by a radial fan. In order to explain the drying behavior of WHs, four different mathematical models were compared and the moisture ratios obtained experimentally and the drying coefficients of models tested were determined by nonlinear regression analysis. The experimental data were fitted into Newton, Page's, Henderson and Pabis and Logarithmic drying models. During the drying period, ambient and drying air temperatures, relative humidity and the losses of mass were measured continuously. The average ambient temperature, air temperature and relative humidity of drying chamber and solar radiation incident were of about 30.3oC, 51.5oC, 36%, 540W/m2, respectively. Drying took place entirely in the falling rate period. The drying rate decreased with increasing drying time and decreasing moisture content. The compressed WH had the shortest drying time than the complete WH samples. The solar drier increased drying rate by about 1.5-2 times, while the drying time decreased by 50% as compared to sun drying samples. The logarithmic model could adequately describe the drying behaviors of complete and compressed WH by multi-tray solar drier and has shown a better fit to the experimental drying data with highest coefficient of determination (0.997) and lowest χ 2, MBE and RMSE. Effective moisture diffusivity values of complete and compressed WH of about 6.65 x 10-8m2/s and 8.16 x 10-8m2/s, respectively. The results obtained are comparable to some of the reported works.