Abstract: The environmental effects of the hygrothermal and UV (ult raviolet) conditions on carbon/bismaleimide composites' static tensile and compressive properties were presented. Specimens with open holes，manufactured by T300/QY8911 laminates，were tested under the environments of normal，hygrothermal，UV and hygrothermal/UV.The moisture absorption tests results indicate that the balance moisture content of the specimens is around 0.6%. The static tests reveal that the tensile strength is hardly affected by the environments. The compressive strength and modulus of the laminates，dominated by the matrix，are reduced by the hygrothermal conditions. The compressive strength of specimen decreases by 6.8% and 20.3% on the condition of 75℃ and 105℃ after moisture absorption，respectively. However，the compressive st rength increases by about 10% after UV exposure (above 300 MJ/m²)，indicating their influence on the composite material is more complex，as interaction of the hygrothermal and UV conditions may exist.