A host-guest compound containing mononuclear univalent Zn+ ions has been prepared through vapor reaction of metallic zinc with protons in the cages of SAPO-CHA, a silicoaluminophosphate molecular sieve. Unlike in fused ZnCl2 salt, the formed Zn+ species are associated with the molecular sieve walls, and this prevents the cations from getting paired to form diamagnetic (Zn-Zn)2+. Electron spin resonance spectroscopy reveals the paramagnetic nature of the Zn+ species which display anisotropic g factors, and the two crystallographically independent Zn+ sites are distinguishable from the ESR signals. The magnetic moments of the univalent zinc in SAPO-CHA interact antiferromagnetically at low temperatures with a Néel point of about 4 K as observed from the temperature dependence plot of the magnetic susceptibility of the host-guest compound.