<正>Martensitic and magnetic transformation behaviors of Ni₅₀Mnln,Ni₄₅Co₅MnIn and Ni_42.5Co_7.5MnIn Heusler alloys were investigated by differential scanning calorimetry （DSC）, vibrating sample magnetometry （VSM） and transmission electron microscopy （TEM）.The martensitic transformation starting temperature （M_s） decreases with increasing In composition, while the Curie temperatures （T_c） of the parent phase are almost independent in each alloy series.On the other hand,the addition of Co resulted in a decrease of the M_s and an increase of the T_c,and degree of the decline of M_s was accelerated by magnetic transformation of the parent phase.The M_s temperature change induced by magnetic field was also confirmed.It was found that the degree of M_s change is strongly related to entropy change by the martensitic transformation which shows a correlation with T_c-M_s.These behaviors can be qualitatively explained on the basis of thermodynamic considerations.