The vertical transport of pesticides from a surface application through an unsaturated porous medium system is of major concern to assess the vulnerability of groundwater contamination. In order to better understand the transport of pesticides in the groundwater, it is essential to understand the flow and predict the pesticide concentration in the unsaturated zone. A one-dimensional numerical model is developed to simulate the transport of pesticides in an unsaturated porous medium, considering the effect of adsorption and microbial degradation with inhibition in addition to conventional advective and dispersive transport. The effect of unsaturated soil parameters on the water flow dynamics and the factors governing the pesticide transport in an unsaturated porous medium is also numerically investigated. The numerical results suggest that the adsorption and biodegradation is an important sink in contaminant removal. In addition, the microbial growth inhibition due to pesticide restricts the potential for biodegradation at low inhibition constant. © 2016 Indian Society for Hydraulics.