动物细胞以分裂形式进行增殖，以适应生长发育、细胞更新和损伤修复的需要。不同的细胞其分裂增殖的频率差异很大，比如增殖频率低甚至不分裂的神经细胞；丧失分裂能力的血液中的成熟红细胞，粒细胞等；增殖频率高的造血干细胞、表皮的基底细胞、胃肠粘膜的上皮细胞等。
动物细胞分裂的方式有3种，即无丝分裂、有丝分裂和成熟分裂。
在有丝分裂中，新的细胞一经产生便开始生长发育和执行其功能，称间期；间期末细胞分裂为2个新细胞的过程称分裂期。两期合称细胞周期或增殖周期。
细胞在间期内主要为细胞分裂做诸多方面的准备，可分3个阶段。
DNA合成前期简称G1期。细胞在此期内主要进行DNA复制所必需的核苷酸、蛋白质和酶类的合成及储备。
DNA合成期简称S期。细胞在此期主要进行DNA的合成，结果使DNA的含量增加一倍，为细胞进入分裂期作重要准备。如果此期受到一些因素干扰就会影响DNA复制，从而抑制细胞分裂或导致变异。
DNA合成后期简称G2期。此期DNA复制虽已结束，但细胞分裂时所需要的RNA和蛋白质等原料，仍需在此期合成。该期还诱发细胞进入分裂期。
分裂期又称有丝分裂期，简称M期。这一时期主要确保染色体能精确均等的分配到2个新细胞内，保持遗传上的一致性。此期可区分为前、中、后、末4个阶段。
前期染色质变为染色体，每条染色体再发展为2条染色单体并在着丝粒处相连；细胞核膨大，核膜及核仁消失；经复制的两个中心体周围出现细丝，称星体，两个中心体之间的细丝形成纺锤体。
中期每条染色体的2个染色单体裂开仍在着丝粒处相连；染色体排列在细胞中央平面上形成赤道板。2个中心体已分别移向两极，纺锤丝与每个染色体着丝粒相连。
后期染色体的着丝粒分裂，染色单体分开随纺锤丝的牵引逐渐移向两极。同时细胞也向两极伸长，中部细胞膜向内凹陷细胞质缩窄。
末期两组染色体不再向两极移动即进入末期。此期染色体恢复染色质状态；核仁、核膜重新出现而形成两个新细胞核；细胞膜中部进一步凹陷使细胞质进一步缩窄变细，最终断裂形成2个新细胞，2个新细胞即进入间期。
Animal cell division under DIC microscope. Here is some information about cell division: Cell division is the process by which a cell, called the parent cell, divides into two cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. In meiosis however, a cell is permanently transformed and cannot divide again. Cell division is the biological basis of life. For simple unicellular organisms such as the Amoeba, one cell division reproduces an entire organism. On a larger scale, cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Cell division also enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by cell division from gametes. And after growth, cell division allows for continual renewal and repair of the organism. The primary concern of cell division is the maintenance of the original cell's genome. Before division can occur, the genomic information which is stored in chromosomes must be replicated, and the duplicated genome separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between "generations".
