Polyamide composite nanofiltration membranes are fabricated under different polymerization time, diamine ratio and organic phase content. The effect of polymerization time on pore size is not significant for reaction times less than 120s but the effective thickness/porosity seems increase drastically even at low polymerization time. Besides, membranes prepared with the addition of 0.05% 3,5-diaminobenzoic acid (BA) shows improvement in terms of flux and exhibits high rejection of divalent salt like metals ion. However, the flux started to reduce at higher BA content because of the decreasing membrane porosity. This means that diamine ratio is a crucial factor to produce an optimum membrane.