The　G-rich　oligonucleotide　T30695　and　T30177　with　the　sequence　of　d(GGGTGGGTGGGTGGGT)　and　d(GTGGTGGGTGGGTGGGT)　can　inhibit　HIV-1　IN　activity　at　nanomolar　concentration　levels.　The　formation　of　G-quadruplex　of　T30695　and　T30177　as　well　as　the　interaction　of　two　natural　alkaloids　berberine　and　sanguinarine　with　G-quadruplex　were　investigated　using　circular　dichroism　spectrometry　and　electrospray　ionization-mass　spectrometry.　The　results　indicated　that　T30695　and　T30177　could　fold　to　form　intramolecular　G-quadruplex　at　low　concentrations　of　NH4OAc.　As　the　concentration　of　NH4OAc　increased　to　40　mM,　the　intramolecular　G-quadruplex　could　be　completely　transformed　to　dimeric　G-quadruplex　for　T30695,　however,　this　concentration　needed　to　be　increased　to　60　mM　for　T30177.　The　inducing　study　illustrated　that　berberine　and　sanguinarine　could　induce　T30695　and　T30177　to　form　intramolecular　G-quadruplex　but　not　dimeric　G-quadruplex.　Berberine　and　sanguinarine　could　bind　to　intramolecular　G-quadruplex,　and　the　relative　binding　affinity　of　sanguinarine　was　greater　than　that　of　berberine　for　T30695,　but　the　two　alkaloids　showed　nearly　identical　relative　binding　affinities　for　T30177.　Berberine　and　sanguinarine　could　also　bind　to　dimeric　G-quadruplex,　and　the　relative　binding　affinity　of　berberine　was　greater　than　that　of　sanguinarine.　Both　berberine　and　sanguinarine　exhibited　good　affinities　toward　intramolecular　and　dimeric　G-quadruplex,　which　may　be　significant　in　the　process　of　G-quadruplex　formation　against　HIV.