The flowering process in plants proceeds through the induction of an inflorescence meristem triggered by several pathways. Many of the genes associated with these pathways encode transcription factors of the MADS domain family. The MADS-domain transcription factor APETALA1 (AP1) is a key regulator of flower development. The first step to understand the molecular mechanisms under the function of each gene in a plant is identification, sequencing and phylogeny analysis of that gene. For this purpose, total RNA was isolated from flower bud of garden cress (Lepidium sativum L.) and was used for cDNA synthesis. The specific primers were designed based on nucleotide sequence alignment of AP1 homologus genes from plants of the same family Brassicaceae and were used in RT-PCR. After observing its electrophoretic pattern and ensuring the quality of PCR product, the amplicon was sent for sequencing. After receiving the results of sequencing, the sequence examined with BLAST, MUSCLE, Gene Runner and MEGA6 softwares. The results indicated amplification of 787 nucleotides fragment that named LsAP1 and was recorded by accession number KP070728 in NCBI database. The studies show high similarity and overlapping of gene bank sequences with LsAP1 illative protein. According to these results, LsAP1 may play a similar role as AP1 in flower induction and could act as a flower meristem identity gene in Lepidium sativum L.