Lettuce (Lactuca sativa L.) is a leading greenhouse-grown vegetable. However, nitrate (NO₃⁻) accumulation in leaves remains a major issue. The aims of this research were: (i) to test the modified intermittent Nutrient Film Technique (NFT) in the cultivation of soilless lettuce in which plants are grown on peat blocks in trays and supplied with an intermittent flow of nutrient solution, and (ii) to calibrate the fertilization scheme to increase yield performance, while keeping NO₃⁻ concentration under control. Two greenhouse trials were performed between autumn 2013 and spring 2014. Results showed that a 30-day cycle is the optimum duration in terms of fresh biomass yield, both for autumn and spring cultivation. Reducing N fertilization in the last cropping days never affected NO₃⁻ concentration in leaves during autumn trial, due to unfavourable growing conditions. Conversely, suspension of fertilization 2 days before harvest had a consistent effect during the spring trial, when NO₃⁻ concentration in leaves was highly reduced (from 20 to 36%) without yield penalties. Thus, suspending fertilization 2–4 days before harvesting in intermittent NFT may reduce, on average, NO₃⁻ accumulation by 29–58% and the fertilization rate by 7–16%, respectively. Yet, growing conditions are crucial to make this system effective.