The effect of three types of organic manures, its combination within and with chemical fertilizer on lettuce production was studied under white net house. Lettuce cv. 'Green Fancy' was grown in December 2003, February, April and June 2004. The same amount of nitrogen (N) from organic manures and chemical fertilizers was applied to the experimental plots in each crop. Cow dung (CD), chicken manure (CM), and duck manure (DM) was applied at 4.5, 4.7 and 5.8 t/ha respectively, which contributed 81 kg nitrogen each. In case of the combination treatments, each combination contributed 1:1 ratio of nitrogen. A treatment with recommended dose of chemical fertilizer (81 kg N/ha) was also included for yield comparison. Fresh weight, dry weight, leaf area, fiber content, dry matter percentage and total yield were considered to evaluate the crop. The application of 4.7 t/ha of chicken manure alone and a combination treatment of chicken manure (2.35 t/ha) plus chemical fertilizer (156 kg of 15-15-15 and 82 kg/ha ammonium sulfate), resulted in higher yield than the other treatments throughout the experiment. However, the combination treatments within organic manure had no influences on yield. There was also no detectable difference on fiber content and dry matter percentage of the crop grown with different treatments and seasons. Soil analysis made after the last crop harvest revealed that the organic treatments reserved more organic matter and other nutrients concentration than chemical fertilizer applied soil. Moreover, the micronutrients content in organic treatment was remarkably higher than the chemical fertilizer applied treatments