The prevalence of religious belief has fallen dramatically. A possible reason is that environmental exposures to previous generations are involved, e.g., evidence of an association between childhood exposures of grandparents and outcomes in their grandchildren including obesity, autistic traits, and survival have been reported. Generally, the associations between the grandparent’s exposure and grandchild’s outcome varied with sex of grandparent, his/her age at exposure and sex of the grandchild.Using data collected by the Avon Longitudinal Study of Parents and Children (ALSPAC) we investigate whether exposures such as smoking and/or traumatic events experienced by any of the grandparents are associated with the likelihood that their adult grandchildren have a religious belief. We show that the granddaughters (but not the grandsons) were more likely to have reported such a belief if one of their maternal grandparents had experienced traumatic events pre-puberty (age 6-11), or their paternal grandmother had experienced such events in adolescence. Conversely if their maternal grandfather had started smoking regularly during childhood or their paternal grandmother had smoked prenatally, the granddaughter was substantially less likely to be a believer. These associations were mutually independent and not explained by demographic factors. They may account for a small proportion of the fall in prevalence of religious belief over time, but the association needs confirming in other studies.