Mammoth Uncensored Word List:
25 words ending with g, 18 letters long

anthropomorphising anthropomorphizing anticounterfeiting compartmentalising compartmentalizing counteradvertising counterinfluencing counterpetitioning counterprogramming counterquestioning disproportionating electrocoagulating hypophysectomizing institutionalising institutionalizing intercommunicating internationalising internationalizing microencapsulating microphotographing nonphosphorylating photolithographing rechromatographing transubstantiating turbosupercharging