Abstract: To provide more dyes with high light fastness for selection for polyester dyeing,thermosol dyeing of polyester fabrics were performed with vat dyes with high light fastness.The effects of dyeing parameters on K/Svalue on polyester fabrics were investigated.The color fastness to rubbing,washing and light on cotton and polyester fabrics dyed with same vat dyes,in which there are similarK/Svalue between them,were compared.The results showed that medium dyeing color depth could be obtained with these vat dyes in thermosol dyeing,and theK/Svalue of polyester fabrics increased with the rising of curing temperature,liquid uptake,dye concentration,and addition of thickening agent and urea to the dyeing liquids.The fastness of rubbing and washing on polyester fabrics dyed with these vat dyes was slightly lower than that on cotton fabrics,while they had similar light fastness.