In an attempt to improve its performance and productivity, a simple low cost modification of stepped-type solar still (SSS) was presented by installing external booster mirrors fixed at its top and bottom edges. The SSS's step width was 4cm and depth of 2cm and black-painted aluminized absorber within area of 0.46 m2. Thus, two SSSs units (conventional without mirrors and modified with same fabricated specifications but with booster mirrors) were investigated at Faculty of Agriculture, Zagazig University, Zagazig, Sharkia Governorate, Egypt in order to assess and compare their performance represented of productivity, indicated temperatures, some thermo-physical properties and daily efficiency under three different water salinity levels of 15000, 35000 and 45000 ppm under solar radiation flux range of 270-1143 and 267-998 W/m2 in case of modified and conventional SSS, respectively, and ambient temperature range of 31.2 to 37.6 oC. The obtained results revealed that, the indicating maximum temperatures gained by modified SSS comparing to the conventional one increased by 14.3, 11.5, 8.6 and 2.5% for glass, water, absorber and vapor, respectively. The daily yielded productively for the modified SSS were 9.91, 7.87 and 6.97 l/m2.d with increase of 84.2, 60.9 and 55.6 % compared to the productivity of the conventional SSS at the previous water salinity levels, respectively. Furthermore, the annual cost of one liter distillate (in EGP; 1 $ = 15.7 EGP) for both conventional and modified SSSs was estimated as (1.33 and 0.88), (1.46 and 1.107) and (1.6 and 1.25) at the same previously mentioned salinity levels, respectively.