A common characteristic of hepatocellular carcinoma in humans and animals is a striking male prevalence. However, the underlying mechanisms remain largely unknown. We have reported that hepatotumorigenesis is prevalent in male H-ras12V transgenic mice (Wang et al., 2005). Orchiectomy and ovariectomy were performed to determine if the presence of sex organ-related factors contributes to hepatotumorigenesis. After orchiectomy and ovariectomy, the mice were sampled at 6 months of age. The pathological diagnosis, sex hormone levels, expression of the H-ras12V transgene, and ras related signal pathways were determined. Orchiectomy significantly reduced the incidence of hepatotumorigenesis in males. However, no significant difference was detected in the incidence of tumorigenesis between ovariectomized and non-ovariectomized females. Molecular biochemical experiments showed that the sex organ-related factors significantly influenced transgene expression, which contributed to activation of the MAPK signaling pathway. The present study demonstrates that testis-related factors play important roles in hepatotumorigenesis in H-ras12V transgenic mice.