Firm moral judgment deems dishonest acts as categorically wrong, and considers any self-serving justification for them as further dishonesty. People, however, commonly use self-serving justifications in order to feel honest even as they behave dishonestly, indicating reduced moral firmness. We test variation in moral firmness by comparing a sample of religious and secular female students. Arguably, religious people’s upbringing and ongoing exposure to moral admonitions promote a firm moral approach which should translate into firmer moral judgments in adulthood. Results of a moral judgment experiment supported this proposition: Religious students judged lies more harshly than secular students, and were less influenced by the availability of self-serving justifications. A moral behavior experiment provided support to the notion that moral firmness in judgment may translate to moral firmness in behavior: whereas modest amount of lying was found among the secular students, no evidence for lying was observed among the religious student. Overall, we provide strong evidence for firm moral judgment among female religious students, and weaker evidence for firm moral behavior. We discuss the relation between firm moral judgment and behavior.