My brother was deported over 15 years ago for a drug conviction, would my mom, who is a US citizen be able to petition for him?

It is very difficult to immigrate someone who has been deported for a drug conviction. I suggest that you bring his entire criminal/immigration files to an immigration lawyer whose practice includes dealing with criminal issues and consult with him or her as to whether your brother has a chance to return and what steps would be involved in doing so. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.