Calcium serves as an important second messenger in many adaptational and developmental processes of plants. The CDPK-related kinases (CRKs) are a type of serinethreonine kinases belonging to the CDPK-SnRK superfamily. In this study, a T-DNA insertion mutant of AtCRK1 (crk1-1) was employed to explore the possible function of AtCRK1 in salt tolerance. Our results indicated that crk1-1 transformants had a decreased tolerance to salt stress during seed germination compared with both wild-type plants and the complemented transgenic lines, in which the full-length genomic AtCRK1 clone with a 2.3 kb promoter was inserted into crk1-1 to drive CRK1 expression under the control of the CRK1 promoter. Furthermore, a higher malondialdehyde (MDA) level and lower free proline content were measured in crk1-1 plants. The qRT-PCR analyses revealed that the transcription of several stress-related genes was decreased in crk1-1 plants. These results indicate that AtCRK1 is involved in the tolerance to salt stress by changing both MDA and proline levels in Arabidopsis, and may act as a positive regulator in the induction of stress-response gene transcription.