An ovulation tester contains: a first body and a second body. The first body is cylindrical and includes a first connecting portion, a first holding disc, and a switch. The switch has a first coupling section which corresponds to a second coupling section of the first body, between the switch and the first holding disc are defined a power supply assembly and a light-emitting element below the power supply assembly, and between the light-emitting element and the first holding disc is defined a light diffuser. The second body is cylindrical and is connected with the first body, the second body includes a second connecting portion for corresponding to the first connecting portion of the first body, a second holding disc for corresponding to the first connecting portion of the first body, and at least one lens in the inner wall thereof below the second holding disc.