This study investigates the effects of the type of advertisement, brand extension, and consumer innovativeness on the credibility of fashion advertisements. The factorial design is constructed as a 2(type of fashion advertisement: general vs. cross-media) × 2(consumer innovativeness: high vs. low) × 2(the type of fashion brand extension: similar vs. dissimilar) three-way mixed design in which consumer innovativeness is the between-subjects variable. Subjects of this study included 210 men and women in their 20s and 30s who resid in Seoul and had SNS experiences. Frequency analysis, credibility analysis, three-way ANOVA, and simple interaction analysis were conducted using the SPSS 20.0 statistics package. The results are as follows: First, the type of fashion advertisement had a significant effect on advertising credibility. Cross-media advertisements had a more positive effect than general advertisements on all of the dependent variables. Also, the type of brand extension and consumer innovativeness showed significant effect on advertising credibility and the interaction effect between the type of fashion advertisement and consumer innovativeness was significant. Lastly, the effect of different types of brand extensions on advertising credibility showed a significant difference according to consumer innovativeness. Thus, a marketing strategy using cross-media advertising is proven to be effective in gaining consumer trust for a fashion brand.