[en] Dry seeds of cotton were implanted with 30 keV nitrogen ion beam of various doses. The injury effects in M₁ generation, the variation frequencies and the variation spectra in M₂ generation, the dose effects and the relationship among them were studied. The irradiation of ⁶⁰Co γ-rays with various doses was used as control. The results indicated that nitrogen ion beam was an effective mutagen for plant breeding. It could induce chromosomal aberration and high frequency of phenotypic variation in M₂ generation. Compared with ⁶⁰Co γ-rays, nitrogen ion beam had local injury effect, higher induced efficiency and wider variation spectra. Higher frequencies of variation with more than one mutated characters in a single plant and quantitative characters were also observed, especially with the dose of 4 x 10¹⁶N⁺/cm². The relationship between variation frequencies of character in M₂ generation and chromosomal aberration frequencies of pollen mother cells in M₁ generation induced by nitrogen ion beam and dosages fitted in with the model Y = A + BX + CX. But when irradiated by ⁶⁰Co γ-rays, the relations fitted in with the model Y A + BX