Maize (Zea mays L.) is a major cereal crop which plays a crucial role in achieving food security in Ethiopia. Maize productivity is limited by low plant population and poor soil fertility management in the country. Hence, a field experiment was undertaken to determine the optimal NPSB fertilizer rate and plant population for maize at Bako. Experiment was designed in split plot design distributing three levels of plant population [53,333 plants ha-1 (25 x75 cm), 66,666 plants ha-1 (60x25cm) and 76923 plants ha-1 (65x20cm)] in the main plots and five levels of NPSB fertilizer rates (0,100,150,200 and 250 kg NPSB ha-1) and recommended NP kg ha-1 rates in sub-plots. The interaction of plant population and NPSB rates influenced significantly (P<5 %) leaf area index, number of cobs plot-1, number of kernel cob-1, dry biomass and thousand kernel weight. The highest number of cob plot-1 (115.3) and dry biomass yield (28,299 kg ha-1 ) were recorded from the treatment 66,666 plant ha-1 with 150 kg NPSB ha-1, and 53,333 plant ha-1 with standard check 92/69 kg NP ha-1, respectively. While highest leaf area index 6.661 was recorded from the combination of 66,666 plants ha-1 with 200 kg NPSB fertilizer rate. The highest grain yield of 9954 kg ha-1 at net profit of 76,038 Birr with marginal rate of return 598% was obtained from 150 kg NPSB ha-1 with 66,666 plants ha-1 (60 cm x 25 cm). Therefore, application of 150 kg NPSB ha-1 with 66666 plants ha-1 can be recommended for farmers in the study area to improve maize productivity.