[Objectives]  The development of resistance to Bt (Bacillus thuringiensis) toxins by Helicoverpa armigera (Hübner) is the main constraint on the continuous planting of Bt transgenic cotton. In order to choose appropriate, alternative Bt genes to incorporate into transgenic cotton, we studied the resistance, and cross-resistance, of H. armigera to different Bt proteins. [Methods]  After successive selection in the laboratory, we obtained 5 Bt-resistant strains with different resistance levels and determined the cross-resistance of these strains to different Bt proteins. [Results]  Selection produced a strain of H. armigera with ultra-high resistance to Cry1Ac but low resistance (tolerance) to Cry2Ab and Vip3Aa. When Cry1Ac-resistant H. armigera were selected for resistance to Cry2Ab or Vip3Aa their resistance to Cry1Ac decreased significantly. Selection could only produce low, or ultra-low, resistance (tolerance) to Cry2Ab or Vip3Aa. The susceptibility of H. armigera to Cry1Ab dropped dramatically in the Cry1Ac-resistant strain, however, its susceptibility to Cry2Ab, Cry2Ah and Vip3Aa did not change significantly. The susceptibility of Cry2Ab-resistant H. armigera to Cry1Ac decreased significantly while the susceptibility of Vip3Aa low-resistant larvae to Cry1Ac did not change. Overall, the present study indicates obvious cross-resistance between Cry1Ac and Cry1Ab, but no cross-resistance between Cry1Ac and Cry2Ah or Vip3Aa. However, asymmetrical cross- resistance was found between Cry1Ac and Cry2Ab. [Conclusion]  The evolution of resistance and cross-resistance in H. armigera should be fully considered when selecting novel, insecticidal genes for transgenic cotton. We suggest that Cry2Ah and Vip3Aa are the best choices for incorporation into new transgenic cotton varieties.