Seal formation at the surface of smectitic soils during rainstorms reduces soil infiltration rate (IR) and causes runoff and erosion. Surface application of dry anionic polyacrylamide (PAM) with high molecular weight (MW) has been found to be effective in stabilizing soil aggregates, and decreasing seal formation, runoff and erosion. The objective of this study was to investigate the effects of surface application of granular PAM (20 kg ha^-1) of two MW (2x10⁵ and 1.2x10⁷ Dalton) together with phosphogypsum (PG) (4 Mg ha^-1) on the IR, runoff and erosion from five smectitic soils ranging in clay content between 8 and 65 percent, during simulated deionized water rainstorms. Spreading dry PAM (both MWs) mixed with PG was effective in increasing soil IR (3-5 times) and reducing erosion (2 - 4 times relative to the control). PAM with moderate MW was as effective as PAM with high MW in its effect on IR and runoff. Conversely, PAM with moderate MW was more effective in reducing soil loss than PAM with high MW. For instance, in the sandy clay, application of amendments resulted in comparable final IR values (15.2 and 15.9 mm h^-1), while soil loss decreased from 838 g m^-2 (in the control) to 371 and 569 g m^-2 for the PAM with moderate and high MW, respectively. Our results were not consistent with former studies on the effects of PAM MW, probably due to differences in the methods of PAM application and soil types.