An efficient synthesis of 5,10-dihydroindeno[1,2-b]indoles (3a-t) containing substituents such as methoxy, hydroxyl, and halogen (F, Cl, and Br) on indeno part was described. Antioxidant and radical scavenging activities of synthesized compounds (3a-t) were determined by various in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH(*)), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radicals (ABTS(*+)), N,N-dimethyl-p-phenylenediamine dihydrochloride radicals (DMPD(*+)), and superoxide anion radicals (O(2)(*-)) scavenging, reducing ability determination by the Fe(3+)-Fe(2+) and Cu(2+)-Cu(+) (CUPRAC method) transformation methods, H(2)O(2) scavenging, and ferrous ion (Fe(2+)) chelating activities. Moreover, these activities were compared to synthetic and standard antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol, and trolox. The results showed that the synthesized compounds (3a-t) had effective antioxidant power.