Declining water resources, low rice yields and a widening gap between current rice demand and production in Zanzibar necessitates a change from the current rice production system to a more efficient system of production such as the system of rice intensification (SRI). In an attempt to evaluate the efficacy of SRI practice and determining the optimum spacing and transplanting age of seedlings for better grain yield, productive tillers and water productivity, a field experiment in a Randomized Complete Block Design (RCBD) was set with 13 treatments and three replications at Bumbwisudi rice irrigation scheme in Zanzibar. The experiment was conducted during vuli season from September 2013 to January 2014. SUPA BC rice variety was transplanted at square spacing (20, 25, 30, 35) cm and 8, 10, 14 and 21 days seedlings ages. Eight days old seedlings, transplanted at 20 x 20 cm spacing (T1) (SRI plot) recorded significantly higher grain yield (7.38 t/ha) as compared to 21 days old seedlings under continuous flooding at 20 cm x 20 cm (T13) (5.283 t/ha). Lower grain yield of (5.14 t/ha) was in older seedling age of 14 days and spacing 25 x 25 cm (T10). There was 39.8% increase in yield in SRI practice compared to continuous flooding. Treatment T5 (10 days old seedling) with 20 x 20 cm spacing produced maximum productive tillers per hill (32/hill). High water productivity was obtained in T5 (0.44 kg/m3) as compared to (0.24 kg/m3) in continuous flooding. Highest water use efficiency (WUE) was observed in T1 (12.06 kg/ha/mm). Amount of water (46.7%) could be saved by using SRI while still producing reasonable yields instead of continuous flooding. Irrigation water analysis in the study area revealed no restriction in its use for rice cultivation. Zanzibar has the potential of increasing yield and water productivity and reducing water use in irrigated rice under SRI.Irish Aid training program