Mulberry (<italic>Morus</italic> <italic>spp</italic>., Moraceae) is a traditional economic crop plant and is also gradually utilized as beverage plants. SWEETs (Sugars Will Eventually be Exported Transporter) are important sugar transporters involved in various biological processes and responses to various stresses. However, SWEETs in mulberry are still poorly studied without a comprehensive functional analysis of <italic>SWEETs</italic>. In the present study, a total of 24 <italic>SWEETs</italic> were identified using <italic>Morus alba (Ma)</italic> genome. Phylogenetic analysis showed that these 24 MaSWEETs were clustered with SWEETs from <italic>Arabidopsis</italic>, <italic>Populus</italic> and <italic>Oryza</italic> and fell into four clades. <italic>MaSWEET</italic>s in the same clade are likely to pose similar intron/exon patterns. These <italic>MaSWEET</italic>s distributed on 12 chromosomes and tandem duplication and block duplication were responsible for the expansion of SWEETs in mulberry. Transmembrane domains and conserved active sites of Tyr and Asp were observed in MaSWEETs. Cis-elements in promoter regions of <italic>MaSWEET</italic>s indicated the possible function of <italic>MaSWEET</italic>s in response to hormones and environment stimulus. <italic>MaSWEET</italic>s showed quite different expression preference in tissues and organs indicating the possible function divergence. In addition, most <italic>MaSWEETs</italic> showed a disturbed expression levels in response to various abiotic stresses and <italic>Ciboria shiraiana</italic> infection. <italic>MaSWEET1a</italic> was functionally characterized as a negative regulator of resistance to <italic>C. shiraiana</italic> infection based on<italic> in vivo</italic> transient overexpression of <italic>MaSWEET1a</italic> in tobacco and down-regulation of <italic>MaSWEET1a/b</italic> in mulberry. Our results provided foundation for further functional dissection of SWEETs in mulberry and a potential regulator for genetic modification.