Phosphorous-containing epoxy resins were prepared from diglycidyl ether of isobutyl bis(hydroxypropyl)phosphine oxide (IHPOGly) and diglycidyl ether of bisphenol A (DGEBA) by crosslinking with 2,4-diaminotoluene. Several IHPOGly/DGEBA molar ratios were used to obtain materials with different phosphorous content. Thermal, dynamomechanical, and flame retardant properties were evaluated and related with the phosphorous content. The weight loss rate of phosphorous-containing resins is lower than that of the phosphorous-free resin for the thermoxidative degradation. Char yields under nitrogen do not show significant differences among the phosphorous-containing resins and the phosphorous-free resin, while under air char yields increase with the phosphorous content. The presence of phosphorous increases the limiting oxygen index (LOI) values even when the phosphorous content is low, and no significant differences with the phosphorous content are observed. V-0 materials were obtained when the resins were tested for ignition resistance with the UL-94 test. (c) 2005 Wiley Periodicals, Inc.