It is *possible* that you may have a claim for discrimination, if the two of you do the same job/have the same title and you also can demonstrate you do more work for him. However, it is not in your favor that he has held that position longer: time in service is a valid and recognized ground for paying employee A more than employee B, even if their positions/titles are the same and B is, in most ways, the better worker.Much will depend on the specific facts: it is one thing is he held the position for 5 more years and is making 20 - 25% more: a differential of 4 - 5% per year of service is not unreasonable. On the other hand, if he was there 1 year longer  and is making 30% more, that suggests sex-based discrimination may be at work. Since many attorneys will provide a free initial consultation to evaluate a case, it would be worthwhile for you to consult with an employment law attorney about the specifics of your situation.