A number of diversely functionalized derivatives of a novel [1,3]selenazolo[4,5‐d]pyrimidine have been synthesized through heterocyclization of some 2,4,5‐trisubstituted‐1,3‐selenazoles with orthoesters in refluxing acetic acid. The synthetic compounds were evaluated for their antimicrobial activity against a panel of microorganisms including Gram‐negative bacteria, Gram‐positive bacteria, and pathogenic fungi. The antifungal results revealed that the new selenium‐containing heterocycles were as good as or sometimes better than terbinafine and fluconazole. The in vitro anticancer activities of aforementioned heterocyclic compounds were screened against human breast carcinoma MCF‐7 and HeLa cervical cancer cells as well as HDF (human dermal fibroblast) normal cells. Antiproliferative results indicated that compounds with piperidine moiety on MCF‐7 cells and with morpholine moiety on HeLa cells exhibited well broad‐spectrum of anticancer activities with 397, 298 and 235 μM and 533, 390 and 204 μM of IC50 values after 24, 48 and 72 h of treatments, respectively, while they had no significant toxic effects on normal cells.