The urban community of Niamey is characterized by a prodigious development of urban and periurban agriculture. Lettuce (Lactuca sativa) is one of the main crops grown in these urban and periurban areas. The aim of this study is to assess the impact of irrigation water on the bacteriological quality of lettuce produced in the market gardening zone of the Niamey city. Three (3) market garden sites were studied (Harobanda (site 1), Gamkallé (site 2) and Gounti yéna (site 3). Eighteen (18) lettuce samples and twenty-nine (29) irrigation water samples were taken from the market garden sites and subjected to microbiological analysis using conventional methods appropriate to each indicator. Thus, five (5) indicators of contamiantion were searched, Total Mesophilic Aerobic Flora (TMAF), total coliforms (TC), faecal coliforms (FC), enterobacteria (Ent), Faecal streptococci (FS), Escherichia coli (E. coli) and Clostridium perfringens (CP).