A field experiment was conduced during the summer seasons of 2005 and 2006 at Disuq district, Kafr El-Sheikh Governorate to study the combined effect of inoculation with Halex-2 (as biofertilizer) and mineral nitrogen levels on cowpea yield and their net return.                 Split plot design was used with four replicates. The main plots were assigned by two treatments of uninoculated (control), and inoculated with Halex-2. Whereas, the sub-plots were assigned by five N levels (0, 10, 20, 30 and 40 kg N fed^-1). Four polynomial quadratic equations were established to show the following results: 1.     The maximum and optimum N rates were decreased as Halex-2 used in the two seasons. 2.     The maximum and optimum cowpea yields were increased as Halex-2 used in the two seasons. 3.     The highest maximum yield (1413.2 kg fed^-1), the highest total value of yield (7065.0 L.E fed^-1) and the highest return of bio and N fertilizer (2936.6 LE fed^-1) were obtained as Halex-2 used in the first season. 4.     The average of efficiency and the efficiency of nitrogen fertilizer at optimum rate were increased as Halex-2 used. 5.     The soil nitrogen content during plant growth (X_s) was increased as Halex-2 added. 6.     The contribution of soil N was increased as Halex-2 used in the two seasons. 7.     The contribution of N fertilizer was increased as N levels increased in the two seasons.