Greenhouse ventilation depends on a large number of parameters such as inside and outside climate and greenhouse and vents designs. They have been intensively studied and incorporated in various global ventilation models. However it depends also strongly on the crop occupying the greenhouse space, mostly for tall crops such as tomato crops. This dependence is particularly important for greenhouse tunnels which lateral openings can be partially obstructed by tomato rows but only very few studies were devoted in the past to this crucial question. Motivated by this important issue, we have systematically studied the effect of tomato crop rows on the ventilation rate of a tunnel type greenhouse. The greenhouse tunnel natural ventilation was studied experimentally by means of a tracer gas method for three stages of tomato crop height: a case (i) without any crop; a case (ii) with a young I m height tomato crop and; (iii) a last case with a mature 2.13 m high tomato crop. The ventilation efficiency dependence of the greenhouse tunnel on crop height, leaf area index and wind direction has been assessed and a numerical relation has been deduced by means of a polynomial correlation.