Textile-based sensors are regarded as an attractive investigation field because they can provide cost-effective, easy to manufacture and disposable devices. In this work we present the activation of multiwalled-carbon nanotubes (MWCNTs) and their deposition on cotton textile for ammonia (NH3) detection. Indeed, COOH terminations of MWCNTs allow for ammonia binding by amide bonds predicating on a resistivity change upon ammonia interaction with the active sites. We found that deposition of MWCNTs caused a homogeneous textile resistance drops (from 1010 Ω to 103 Ω) with respect to the pristine cotton sample. Monitoring of the resistance variation over time after pipetting the analyte suggest an initial ammonia diffusion throughout the porous CNTs film deposited over the textile which determines a resistance increase and a subsequent resistance reduction due to the ammonia high volatility. These results suggest the feasibility of MWCNTs deposited on cotton fabric as sensor for ammonia detection.