A variety of novel 3-butyl-2-substituted amino-3H-quinazolin-4-ones were synthesized by reacting the amino group of 3-butyl-2-hydrazino-3H-quinazolin-4-one with various aldehydes and ketones. The title compounds were investigated for analgesic, anti-inflammatory and ulcerogenic index activities. The compound 3-butyl-2-(1-methylbutylidene-hydrazino)-3H-quinazolin-4-one (AS3) emerged as the most active analgesic agent. Compound 3-butyl-2-(1-ethylpropylidene-hydrazino)-3H-quinazolin-4-one (AS2) emerged as the most active anti-inflammatory agent and is moderately more potent when compared to the reference standard diclofenac sodium. Interestingly, the test compounds showed only mild ulcerogenic potential when compared to aspirin.