The field experiment to evaluate the effectiveness of bean plant population under conservation and conventional tillage systems in suppressing weeds in maize-bean intercropping systems was conducted at the Tropical Pesticides Research Institute (TPRI) for the 2010 short rains and 2011 long rains season. A split-split plot experiment laid out in a Randomized Complete Block Design (RCBD) was used with three replications. The main treatments were: the conventional and conservation tillage systems, having five sub plot factors namely: sole maize, sole bean, maize-bean intercrops at a constant maize spacing of 75cm x 30 cm and a varied spacing of bean at 75cm x 20cm, 50cm x 20cm and 25cm x 20cm. The sub-sub plot factors were four weed management practices namely: weeding once at 28 days after planting, pre-emergence selective herbicide application without weeding, weeding twice at 14 and 28 days after planting, and control (i.e. without weeding). Data were analyzed by Gen-stat software and means were separated by Tukey’s Honestly Significant Differences Test (THSDT). The results showed that maize intercropped with bean at a spacing of 50cm x 20cm gave significantly higher grain yield (5.1 t/ha) while maize grown as a sole crop gave lowest grain yield (3.3 t/ha) during the 2010 short rains season. For the long rain season, maize intercropped with bean at a spacing of 50cm x 20cm resulted in a significantly higher grain yield (4.8 t/ha) while maize grown as a sole crop gave significantly lower grain yield (3.7 t/ha) during the 2011 long rains season. The use of pre-emergence selective herbicide resulted in an increased yield of both maize and beans in both seasons. The conventional tillage showed superiority in controlling weeds than conservation tillage. Bean intercropped at 50cmx20cm was the best bean population for suppressing weeds without affecting maize yield.Alliance for Green Revolution in Africa (AGRA)