Success in applying precision agriculture to cotton production depends strongly upon intensive scouting and a full understanding of the variability of soil and plant parameters in cotton fields. While cotton yield variation has been examined extensively by many researchers, only a few studies have attempted to document the variability of cotton fiber quality at the production level. In-season soil moisture content (water availability) is a major determiner of cotton fiber quality. The objective of this study was to examine the spatial variability of cotton fiber quality and soil moisture content in both irrigated and dry-land cotton fields. This experiment was conducted on the 321.9-ac. Impact Center Research Farm of Texas A&M University . Three 0.75-ac. regular grids were laid out in both irrigated and dry-land areas. A total of 86 sampling points (40 irrigated and 46 non-irrigated) were selected from the grids for data collection. At each sampling point, soil moisture content was measured and recorded weekly from seedling to boll maturation. Seedcotton was hand picked, ginned with a laboratory saw gin, and subjected to HVI testing to obtain fiber quality measurements. Univariate statistical methods were applied to explore the soil moisture content and cotton fiber quality variations. Post-harvest cotton fiber quality was compared between irrigated and dry-land cotton. The hypotheses to be tested in this study were as follows: 1) significant variability exists in both post-harvest cotton fiber quality and in-season soil moisture content, 2) fiber quality of dry-land cotton is significantly different from that of irrigated cotton, and 3) in-season soil moisture content has a significant effect upon post-harvest cotton fiber quality. The existence of great variability in soil moisture content and cotton fiber quality, as well as their cause and effect association, would justify management zone development and variable rate water application for cotton fiber quality optimization.